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Edexcel ScienceiGCSE Physics

G. Fundamentals of Circuits

2019-2020

Name:________________Physics Teacher:______________

House CG

Year 9

Specification Checklist

2.01 use the following units: ampere (A), coulomb (C), joule (J), ohm (Ω), second (s),

volt (V) and watt (W)

2.04 know and use the relationship between power, current and voltage:

power = current × voltage

P = I × V

and apply the relationship to the selection of appropriate fuses

2.05 use the relationship between energy transferred, current, voltage and time:

energy transferred = current × voltage × time

E = I × V x t

2.07 explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting

2.08 understand how the current in a series circuit depends on the applied voltage and the number and nature of other components

2.09 describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how to investigate this experimentally

2.10 describe the qualitative effect of changing resistance on the current in a circuit

2.11 describe the qualitative variation of resistance of light-dependent resistors (LDRs)

with illumination and thermistors with temperature

2.12 know that lamps and LEDs can be used to indicate the presence of a current in a

circuit

2.13 know and use the relationship between voltage, current and resistance:

voltage = current × resistance

V = I × R

2.14 know that current is the rate of flow of charge

2.15 know and use the relationship between charge, current and time:

charge = current × time

Q = I × t

2.16 know that electric current in solid metallic conductors is a flow of negatively charged electrons

2Fundamentals of Circuits – Science (Physics)

2.17 understand why current is conserved at a junction in a circuit

2.18 know that the voltage across two components connected in parallel is the same

2.19 calculate the currents, voltages and resistances of two resistive components

connected in a series circuit

2.20 know that:

• voltage is the energy transferred per unit charge passed

• the volt is a joule per coulomb

2.21 know and use the relationship between energy transferred, charge and voltage:

energy transferred = charge × voltage

E = Q × V

2.22 identify common materials which are electrical conductors or insulators,

including metals and plastics


Key Definitions

Key Word Image Definition

Charge The physical property of matter that causes it to experience a force when placed in an E-M field. There are two types of electric charges; positive and negative

Component Devices that can be selected individually and put together to make a circuit.

Conductor A material that permits electrons to flow freely from particle to particle thus allowing electricity to flow through.

Current The rate of flow of charge.

It has the symbol ‘I’ and is measured in Amps (A).

Fuse A short length of wire designed to melt and separate in the event of excessive current.

Insulator A material that does not permit electrons to flow freely from particle to particle thus preventing electricity from flowing through.

Junction A point where at least three circuit paths meet.

Light dependent resistor

A type of resistor which has a resistance that changes with the amount of Illumination it is exposed to.

Parallel Circuit A closed circuit in which the current divides into two or more paths before recombining to complete the circuit.

Resistance A measure of how hard it is to produce a big current in a circuit.

Series Circuit A closed circuit in which the current follows one path

Thermistor A type of resistor which has a resistance that changes with the temperature it is exposed to.

Voltage The energy transferred per unit charge passed.

It has the symbol ‘V’ and is measured in Volts (V).


1: Circuits, Current and Charge

Component Symbols

How many component symbols do you already know? Add these with pencil. Complete the rest of the table with your teacher.

Component Name Component Symbol Component Name Component

Symbol

Light Bulb (Fixed) Resistor

Switch Variable Resistor

Wire Fuse

Power Supply (AC) Diode

Voltmeter Light Emitting Diode (LED)

Ammeter Light Dependent Resistor (LDR)

Cell Thermistor

Battery Heater

Motor Generator

YOU MUST MEMORISE THESE SYMBOLS


Learning Outcomes:

1. Identify at least 8 component symbols and put them together to draw a circuit diagram.

2. Describe Current as the rate of flow of negatively charged particles through a circuit.

3. Use and memorise the equation linking Charge, Current and Time.

Drawing Circuits

When we draw circuits we always draw them as ‘rectangles’ rather than circles. This makes them easier to read (especially when they become complicated later on).

Worked Example

Draw the following circuit using a circuit diagram and correct component symbols:


What is Current?

Key Ideas

1. Current has the symbol ‘I’ and is measured in Amps (A)2. Current is defined as the ‘Rate of flow of charge’ (charge per second)3. Electrical current always flows from the positive terminal of the Power Supply to the

negative terminal of the Power Supply. 4. For a current to flow the circuit must be made from a conductor and there must be a

complete circuit.


What is Charge?

Key Ideas

1. Charge has the symbol ‘Q’ and is measured in Coulombs (C)2. Charge, Current and times are linked in the following equations:

Charge=Current ×time3. To use this equations Current must be measured in ‘Amps’ (A) and Time must be

measured in ‘Seconds’ (s).

Worked Examples

1. How much charge has passed if 5A of current flows around a circuit for 15 seconds?

2. How long does it take a current of 3A to transfer 90C of charge?


Worksheet – Charge, Current and Time

Complete the questions below using the equation you have just learnt. You must show all of your working [equation, substitution, solution and units]

1. What charge passes if 4A flows for 20s?

…………………..

2. What charge passes if 7A flows for 30s?

…………………..

3. What charge passes if 2A flows for 2 minutes?

…………………..

4. What current flows is 100C passes in 10s?

…………………..

5. What is the current when 120C if charge flows through a cell in 20s?

…………………..

6. What is the current when 20,000C of charge flows through a lamp in 1800s?

…………………..

7. How long does it take for a current of 1A to transfer 90C of charge?

…………………..


8. What is the current when 500,000C of charge flows in 1 hour?

…………………..

9. How much charge flows through a cell when a current of 5A flows for 10 minutes?

…………………..

10. How long does it take for current of 5A to transfer 1,000,000C of charge?

…………………..

11. For how many hours can a power supply provide a current of 0.01A if it stores 144C of charge?

…………………..

12. A certain type of rechargeable battery is capable of delivering 0.2A of current for 4000s, before its voltage drops and it needs to be recharged. Calculate:

a. The total charge the battery can deliver before it needs to be recharged.

…………………..

b. The maximum time it could be used without being recharged if the current through it were 0.5A.

…………………..

13. In a lightening flash a typical amount of charge which reaches the Earth is 10C. If the flash lasts for 0.5ms, what is the average current?

…………………..


2: Current in Circuits

Revision Check: Circuit Diagrams

Using your knowledge from last lesson can you construct the following circuits?

1. 5 bulbs connected to a battery with one switch which turns all bulbs on and off together.

2. 5 light bulbs connected to a battery with enough switches to turn them on and off individually

Now add arrows to each diagram to show the direction that current is flowing in.


Learning Outcomes:

1. Describe the difference between series and parallel circuits.2. Measure current using an ammeter and use a bulb to indicate that current

is flowing3. Explain how current behaves in a series and parallel circuit

Parallel vs. Series


G1: Investigation – Current in series and parallel

In this investigation you are going to see if you noticeany patterns when you measure the current in the 2different types of circuit. The two types of circuit are:

1. 2.

We will use an ________________ to measure current.

Method:

1. Set up the circuit as per the diagram2. USE A POWER SUPPLY SET TO 6V DC3. Make sure your variable resistor is set to maximum resistance4. Take readings from the ammeters5. Reduce the resistance of the variable resistor6. Repeat steps 3 and 47. Note your observations.

Current in Series

Set up the following circuit:

Why do we put a bulb in the circuit?

…………………………………………….

…………………………………………….

…………………………………………….

Add your results to the tables below:

Meter Current [A]

Meter Current [A]

Meter Current [A]

Meter Current [A]

A1 A1 A1 A1

A2 A2 A2 A2

A3 A3 A3 A3


A3

A2

A1

Health and Safety Check!

Keep hands dry and make sure all equipment is in good working order

Do you notice any patterns in your results for each table?

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

Current in Parallel


Add your results to the tables below:

Meter Current [A]

Meter Current [A]

Meter Current [A]

Meter Current [A]

A1 A1 A1 A1

A2 A2 A2 A2

A3 A3 A3 A3

A4 A4 A4 A4


……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………


A4

A3

A2

A1

Current in Series and Parallel

Key Ideas

1. Current is the same everywhere in a series circuit.2. Current ‘splits’ at the junction in a parallel circuit.

Worked Examples

1.

2.


Worksheet: Current in Series and Parallel

Can you work out the missing Ammeter reading? Assume all bulbs have the same resistance. [Hint: You may need to look at how many cells are in the battery to help you!]


1.35A

1.20A

3: Voltage

Knowledge and Understanding QuizUse the knowledge you gained in the previous lessons and since the start of Shell to answer the following questions.

1. In what direction does Friction act?

……………………………………………………………… (1)

2. What is the definition of a Galaxy and can you give an example?

………………………………………………………………………………………… (2)

3. An object exert a force of 600N over an area of 0.34m2. How much pressure does it

produce?

(3)

4. In the space below, sketch a circuit connected to a battery which has a heater and

thermistor in parallel with each other.

(4)

5. What is the equation linking frequency, wavespeed and wavelength?

(1)

Score [ /11]


Learning Outcomes:

1. Define Voltage (potential difference)2. Describe how Voltage behaves in a series and parallel circuits 3. Explain, with reference to voltage, the advantages of using a parallel circuit

over a series circuit.

What is voltage?

Key Ideas

1. Voltage has the Symbol ‘V’ and is measured in Volts (V)2. Voltage is defined as the energy transferred per unit charge passed3. Voltage is measured across a component in a circuit using a Voltmeter4. A Voltmeter must always be connected in Parallel


G2: Investigation – Voltage in series and parallel

In this investigation you are going to see if you noticeany patterns when you measure the voltage in the 2different types of circuit. The two types of circuit are:

1. 2.

We will use an ________________ to measure voltage.

Method:

1. Set up the circuit as per the diagram2. USE A POWER SUPPLY SET TO 6V DC3. Make sure your variable resistor is set to maximum resistance4. Take readings from the voltmeters5. Reduce the resistance of the variable resistor6. Repeat steps 3 and 47. Note your observations.

Hint: Add the Voltmeters to your circuits after you have build the main “loop”.

Q: How would you connect the voltmeter across the light bulb in the circuit below?




Voltage in Series


What do you notice about how the

voltmeters are connected?

…………………………………………….

…………………………………………….

…………………………………………….

Add your results to the tables on the next page.

Meter Voltage [V]

Meter Voltage [V]

Meter Voltage [V]

Meter Voltage [V]

V1 V1 V1 V1

V2 V2 V2 V2

V3 V3 V3 V3


……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………


32

1

Voltage in Parallel


Add your results to the table below:

Meter Voltage [V]

Meter Voltage [V]

Meter Voltage [V]

Meter Voltage [V]

V1 V1 V1 V1

V2 V2 V2 V2

V3 V3 V3 V3

V4 V4 V4 V4


……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………


4

2

1

3

Summary: Voltage in Series and Parallel

Key Ideas

1. Voltage is the same across every branch of a parallel circuit.2. Voltage is shared among components in a series circuit3. The advantage of using a Parallel circuit for lighting is that all bulbs will end up with

the same brightness.

Worked Examples:

1.

2.


Worksheet – Voltage in Series and Parallel

Find the missing values in the voltmeters. Assume all bulbs have the same resistance.

Now create your own example below [get creative!]:


4: Resistance and Ohms’ Law

Knowledge and Understanding QuizUse the knowledge you have gained in the previous 3 lessons to answer the following questions:

1. What is the symbol for Current?

……………………………………………………………… (1)

2. What do we measure Current in and how would we measure it?

………………………………………………………………………………………… (2)

3. Draw the following 4 circuit symbols:

Resistor Voltmeter Thermistor LED

(4)

4. What is the equation linking Charge, Current and Time?

………………………………………………………………………………………… (1)

5. Give 2 advantages of using a parallel circuit over a series circuit.

…………………………………………………………………………………………

………………………………………………………………………………………… (2)

Score [ /10]


Learning Outcomes:

1. Define Resistance (R) and know that is is measured in Ohms ()2. Memorise and use the equation for Ohms’ Law:

Voltage=Current× Resistance3. Describe and carry out an investigation to find the resistance of a resistor.

What is Resistance?

Key Points

1. Resistance is a measure of how hard it is to produce a big current in a circuit. 2. Resistance has the symbol ‘R’ and is measures in ‘Ohm’s’ (). 3. The more components you add to a circuit, the higher the resistance. 4. Resistance can be calculated in series by simply adding the individual resistances

of each component. RT=R1+R2+…


Ohms’ Law

Key Ideas

1. Voltage, Current and Resistance are linked in the following equations:Voltage=Current× Resistance

2. To use this equation Voltage must be measured in ‘Volts’ (V), Current must be measured in ‘Amps’ (A) and Resistance must be measured in ‘Ohms’ ().

3. Sometimes, questions that use Ohm’s law come in the form of a circuit. You may need to use what you have learnt about the behaviour of voltage, current and resistance in circuits to help you with these.

Worked Examples:

1. What voltage is required to pass a 3A current through a 6 resistor?

2. What is the resistance of a resistor if it allows 5A of current to pass through when connected to a 10V Power supply?

Worksheet – Using Ohms’ Law



1. Calculate the voltage required to cause a current of 3A to flow through a resistance of 5Ω.

…………………..


…………………..


…………………..

4. Calculate the resistance if a voltage of 6V causes a current of 2A.

…………………..


…………………..

6. Calculate the current flowing when a voltage of 6V is connected across a 2Ω resistor.

…………………..

7. Calculate the current flowing when a voltage of 20V is connected across a 5Ω resistor.


…………………..


…………………..

9. In the circuit below R1 is 60Ω and R2 is 40Ω. The cell is providing a voltage of 12V to the circuit:

a. Label the information in the question on to the diagram. b. Calculate the total resistance in the circuit.

c. Calculate the current in the circuit.

d. Calculate the voltage across R1

e. Calculate the voltage across R2

10. Find the value of R:


G3: Investigation – Finding Resistance (Resistor)

In this investigation you are going to find out the resistance of an unknown resistor. In order to calculateresistance you need to measure 2 quantities:

Once you have measured these you can calculate resistance using the following formula:

Method:

1. Set up the circuit as per the diagram.2. USE A POWER SUPPLY SET TO 6V DC3. Make sure your variable resistor is set to maximum resistance4. Take readings from the voltmeter and ammeter 5. Reduce the resistance of the variable resistor6. Repeat steps 3 and 4 until you have filled up the table

(try to space out your readings evenly on the variable resistor)7. Calculate resistance

Add Units to the table headings:

Current [ ] Voltage [ ] Resistance [ ]

Questions:




1. Did the resistance of the resistor change as the voltage and current changed?

…………………………………………………………………………………………

2. How do your results show this?………………………………………………………………………………………… …………………………………………………………………………………………

3. Does it matter which way round you put your resistor in the circuit?

…………………………………………………………………………………………

4. What was the value of Resistance for your resistor?

5. Plot your results in a graph (Current on the y-axis and Voltage on the x-axis) and stick it below:

6. Add a line of best fit to your results.

7. Describe the shape of the graph you have plotted.

………………………………………………………………………………………… ………………………………………………………………………………………… …………………………………………………………………………………………

5: I-V Curves


Knowledge and Understanding QuizUse the knowledge you gained in the previous lessons and since the start of Shell to answer the following questions.

1. How must an ammeter be connected?

……………………………………………………………… (1)

2. What is the centre of gravity?

………………………………………………………………………………………… (2)

3. The time base on the oscilloscope trace below is 3ms. What is the frequency of the

signal?

(3)

4. In the space below, sketch a circuit which has a resistor connected to a cell.

Add a voltmeter to the circuit to measure the voltage across the resistor.

(4)

5. What are the two common units used for density?

……………………………………………………………… (2)

Score [ /12]


Learning Outcomes:

1. Identify the correct way to connect a diode in a circuit2. Describe and carry out an investigation to find the I-V curves for a wire, a light

bulb and a diode3. Identify and Sketch the I-V curves for a resistor, wire, light bulb and diode

Component Information: The Diode

Key Points

1. Unlike the other components you have come across, the diode must be connected the right way round (otherwise it will not work)

2. The silver/grey band on the diode should be pointing to the negative terminal of the power supply

3. The ‘arrow’ shape in the diode symbol should follow the direction of the current in the circuit.


G4: Investigation – I-V Curves

In this investigation you are going to measure the current and voltage across different components then plot a graph of current against voltage.

What will go on the…

y-axis: _____________________

x-axis: _____________________

Method:

1. Set up the circuit as per the diagram for each component2. NOTE THE VALUE REQUESTED FOR THE POWER SUPPLY3. Make sure your variable resistor is set to maximum resistance4. Take readings from the voltmeter and ammeter 5. Reduce the resistance of the variable resistor6. Repeat steps 3 and 4 until you have filled up the table

(try to space out your readings evenly on the variable resistor)7. Calculate resistance8. Plot the I-V curve for that component9. Once you have finished. Summarise your findings below.

Summarising your Results

Sketch the shape of your 3 I-V curves below.




I I I

V V VTHE WIRE/RESISTOR THE LIGHT BULB THE DIODE

The Wire



I-V Curve for the wire

Describe the shape of your graph

……………………………………………………………………………………………………………


4V

Graph Checklist

Axes Labels (inc. units)

AppropriateScale

Points Plotted

Line of BestFit

The Light Bulb



I-V Curve for the light bulb


……………………………………………………………………………………………………………


12V

Graph Checklist


AppropriateScale

Points Plotted

Line of BestFit

The Diode



I-V Curve for the diode


……………………………………………………………………………………………………………

At what voltage does the diode appear to “turn on”? ………………………


2V

Graph Checklist


AppropriateScale

Points Plotted

Line of BestFit

6: LDRs and Thermistors

Investigation Write-Up Practice

Describe an experiment to investigate how the extension of a spring is affected by the force

applied to it. Your write-up should include:

Equipment used for each measurement

Instructions to be followed during the investigation including any relevant graphs to

be plotted.

Steps that should be taken to ensure accurate results.

You may draw a diagram to support your answer.

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

Score [ /6]



Learning Outcomes:

1. Identify and Sketch the Component Symbols for LDRs and Thermistors2. Describe and carry out an investigation to find out how the resistance of LDRs

and Thermistors vary with illumination and temperature respectively.3. Sketch and interpret the resistance curves for LDRs and Thermistors

Component Information: The LDR and Thermistor

Key Points

1. The resistance of an LDR varies with illumination (brightness of the light it is exposed to)

2. The resistance of a Thermistor varies with temperature3. Both can be connected either way round.


G5: Investigation – LDR

In this investigation you are going to be calculatingthe resistance of an LDR with varying illumination.

To calculate resistance I need to measure:

1.2.

Once you have measured these you can calculate resistance using the following formula:

Method:

1. Set up the circuit as per the diagram 2. SET THE POWER SUPPLY TO 6V DC3. Vary the amount of light (illumination) that the LDR is exposed to

[This can be done by moving up from complete darkness (LDR covered up) to total brightness (direct light from torch)]

4. Take readings from the voltmeter and ammeter 5. Repeat steps 3 and 4 until you have filled up the table

(try to space out your readings evenly as possible – this will be tricky!)6. Calculate resistance.

ResultsAdd Units to the table headings:

Current [ ] Voltage [ ] Resistance [ ] Illumination [6-bright, 1-dull]




Be careful when working in the dark

Questions

1. Plot a graph of Resistance against Illumination (Resistance on the y-axis and Illumination on the x-axis)

2. Use your graph to describe how Illumination affects the resistance of an LDR.

…………………………………………………………………………………………

…………………………………………………………………………………………

3. Can you think of a way an LDR could be used in the real world that would take

advantage of this property?

…………………………………………………………………………………………

…………………………………………………………………………………………

…………………………………………………………………………………………

…………………………………………………………………………………………

…………………………………………………………………………………………

…………………………………………………………………………………………


Graph Checklist


AppropriateScale

Points Plotted

Line of BestFit

G6: Demo – Thermistor

In this investigation you are going to be calculatingthe resistance of a Thermistor with varying temperature.

What will you be using to measure temperature?

…………………………………………

In this experiment you are going to be using a water bath. Describe below how you will vary the temperature of the water bath.

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

Method:

1. Set up the circuit as per the diagram 2. SET THE POWER SUPPLY TO 6V DC3. Vary the temperature of the thermistor using your method above.4. Take readings from the voltmeter, ammeter and thermometer.5. Repeat steps 3 and 4 until you have filled up the table

(try to space out your readings evenly as possible – this will be tricky!)6. Calculate resistance.


Temperature [ ] Current [ ] Voltage [ ] Resistance [ ]




Water bath will be hot.

Questions

1. Plot a graph of Resistance against Temperature (Resistance on the y-axis and Temperature on the x-axis)

2. Use your graph to describe how temperature affects the resistance of a thermistor.

…………………………………………………………………………………………

…………………………………………………………………………………………

3. Can you think of a way a thermistor could be used in the real world that would take

advantage of this property?

…………………………………………………………………………………………

…………………………………………………………………………………………

…………………………………………………………………………………………

…………………………………………………………………………………………

…………………………………………………………………………………………

…………………………………………………………………………………………


Graph Checklist


AppropriateScale

Points Plotted

Line of BestFit

7: Energy in circuits

Knowledge and Understanding QuizUse the knowledge you have gained in the previous 6 lessons to answer the following questions:

1. What is the unit of Charge?

……………………………………………………………… (1)

2. What is the equation liking Voltage, Current and resistance?

………………………………………………………………………………………… (2)

3. Draw the following 4 circuit symbols:

LDR Diode Battery Heater

(4)

4. Sketch the IV curves for the following components. Wire Diode Light Bulb

(3)5. What happens to the resistance of a Thermistor when you increase the temperature

it is exposed to?

………………………………………………………………………………………… (1)

Score [ /10]


Learning Outcomes:

1. Describe the energy transfers that occur in a circuit.2. Memorise and use the equation linking Energy, Charge and voltage:

Energy=Charge×Voltage3. Derive and use the equation linking Energy, Current, Voltage and time:

Energy=Current×Voltage×Time

Energy

Key Ideas

1. As the charges flow around a circuit the energy they carry is transferred by the components they pass through.

2. Energy, Charge and Voltage are linked in the following equation:Energy=Charge×Voltage

3. To use this equation Voltage must be measured in ‘Volts’ (V), Charge must be measured in ‘Coulombs’ (C) and Energy must be measured in ‘Joules’ (J).

Worked Examples:

1. How much energy is transferred when the potential difference is 120 V and the

charge is 2 C?

2. What is the voltage when 25J of energy is transferred through a circuit with a charge

of 2C?


Worksheet – Energy and Charge


1. How much energy is transferred when 10C flows through a lamp with 230V applied across it?

…………………..

2. How much energy is transferred when 15C flows through a lamp with 2V applied across it?

…………………..

3. How much energy is transferred when 0.5C flows through a lamp with 230V applied across it?

…………………..

4. How much energy is transferred when 10.7C flows through a circuit with 3V applied across it?

…………………..

5. How much energy is transferred when 42C flows through a circuit with 230V applied across it?

…………………..

6. What is the charge when 20J of energy is transferred through a lamp with 230V applied across it?

…………………..

7. What is the voltage when 100J of energy is transferred through a circuit with a charge of 10C?

…………………..



…………………..

9. What is the voltage when 1000J of energy is transferred through a circuit with a charge of 3C?

…………………..


…………………..

11. What is the charge when 25kJ of energy is transferred through a lamp with 6V applied across it?

…………………..

12. What is the voltage when 3.4kJ of energy is transferred through a circuit with a charge of 7C?

…………………..

13. How much energy is transferred when 2.9C flows through a lamp with 1.2V applied across it? Give your answer in kJ.

…………………..

14. What is the voltage (in kV) when 135J of energy is transferred through a circuit with a charge of 1.3C?

…………………..Derving E=IVt


Key Ideas

1. Charge is linked to current by the equationCharge=Current ×Time

2. This can be used to derive the equationEnergy=Current×Voltage×Time

Worked Examples:

1. How much energy is transferred when the potential difference is 120 V a current of

4A is allowed to flow for 10s?

2. How long will it take a current of 4A to transfer 100J of energy if connected to

a 6V power supply?

Worksheet – Energy, Current, Voltage and Time



1. How much energy is transferred when 10A flows through a lamp with 230V applied across it for 25s?

…………………..

2. How much energy is transferred when 5A flows through a lamp for 100s with 2V applied across it?

…………………..

3. How much energy is transferred when 3A flows through a resistor for 2 minutes with 230V applied across it?

…………………..

4. What voltage is required for a 6A current to produce 600J of energy in 25s?

…………………..

5. What current is required to supply 1kJ of energy to a lamp in 100s if a 230V is applied across it?

…………………..

6. How long will it take a 4A current to supply 200J of energy when connected to a 6V supply?

…………………..

7. What current is required to supply 5kJ of energy to a lamp in 5 minutes if a 20mV is applied across it?

…………………..

8: Power in circuits


Energy Transfers in CircuitsCan you identify the useful and wasted energy outputs for the following components?

Useful: Useful: Useful:

Wasted: Wasted: Wasted:

BUZZER LOUDSPEAKER

Useful: Useful: Useful:

Wasted: Wasted: Wasted:


Learning Outcomes:

1. Know that Power (P) is measured in Watts (W)2. Describe power as the rate at which electrical energy is transferred.

3. Memorise and use the equation linking Power, Current and VoltagePower=Current×Voltage

Power

Key Ideas

1. Electrical Power measures the rate at which electrical energy is transferred (usually turned into heat).

2. Power, Current and voltage are linked in the equationPower=Current×Voltage

3. To use this equation Voltage must be measured in ‘Volts’ (V), Current must be measured in ‘Amps’ (A) and Power must be measured in ‘Watts’ (W).

Worked Examples:

1. How much Power is supplied to a light bulb connected to a 25V supply if a current of

0.2A flows?

2. A new LED has a power of 2.5W. It is connected to a mains supply at 230V. How

much current flows through the bulb?


Worksheet – Power, Current and Voltage


1. Calculate the power of an electric fire that requires a current of 13A for a voltage of 230V.

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2. Calculate the power of a television that requires a current of 2A for a voltage of 230V.

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3. Calculate the current drawn when a microwave of power 690W is connected to a 230V supply.

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4. Calculate the current drawn when a kettle of power 2000W is connected to a 230V supply.

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5. Calculate the voltage required by an electric fire of power 2200W and current 20A.

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6. Calculate the voltage required by a light bulb of power 24W and current 4A.

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7. Calculate the current drawn when a cooker of power 4 kW is connected to a 230V supply.

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8. Calculate the Power when a cooker draws 6mA of current from a 230V supply.

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Fundamentals of Circuits

Past Paper Questions


Q1. A washing machine has an electric motor and an electric heater.

The resistance of the heater is 22 Ω.

The mains voltage is 230 V.

(a) (i) State the equation linking voltage, current and resistance.(1)

(ii) Show that the current in the heater is about 10 A when it is working.(2)

(Total for question = 3 marks)


Q2.

A light dependent resistor (LDR) can be used as a sensor to detect light intensity.

Describe how the resistance of an LDR varies as the light intensity changes.

You may sketch a graph to help your answer.

(3)

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Q3.

A student investigates how the resistance of a piece of wire changes with voltageacross the wire.

The student connects an ammeter, a voltmeter, a battery, a variable resistor and thewire in an electrical circuit.

(a) (i) Complete the diagram to show how the student should connect the circuit.(3)

(ii) Describe what she should do to obtain a set of results for her investigation.(3)

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(b) The student keeps the temperature of the wire constant during the investigation.(i) Suggest why she does this.

(1)


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(ii) Suggest how she does this.

(1)

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(c) When the student looks at her results, she notices that the voltage across the wireis directly proportional to the current in it.

(i) State the relationship linking voltage, current and resistance.(1)

(ii) The student calculates the resistance and then plots a graph of resistanceagainst voltage.

On the axes, sketch the shape of her graph.(1)



Q5.

A student investigates how the resistance of a thermistor varies with temperature.

(a) Draw the circuit symbol for a thermistor.(1)

(b) The student uses voltmeter and ammeter readings to find the resistance at eachtemperature.

One set of readings is shown below.

(i) State the equation linking voltage, current and resistance.(1)

(ii) Show that the resistance of the thermistor at 80 °C is about 5000 Ω.(3)

(Total for question = 5 mark)


Fundamentals of Circuits

Spec Point Notes


Specification Notes – Fundamentals of Circuits

2.01 use the following units: ampere (A), coulomb (C), joule (J), ohm (Ω), second (s),

volt (V) and watt (W)

2.04 know and use the relationship between power, current and voltage:

power = current × voltage

P = I × V

and apply the relationship to the selection of appropriate fuses


2.05 use the relationship between energy transferred, current, voltage and time:

energy transferred = current × voltage × time

E = I × V x t

2.07 explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting

2.08 understand how the current in a series circuit depends on the applied voltage and the number and nature of other components


2.09 describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how to investigate this experimentally

2.10 describe the qualitative effect of changing resistance on the current in a circuit

2.11 describe the qualitative variation of resistance of light-dependent resistors (LDRs)

with illumination and thermistors with temperature


2.12 know that lamps and LEDs can be used to indicate the presence of a current in a

circuit

2.13 know and use the relationship between voltage, current and resistance:

voltage = current × resistance

V = I × R

2.14 know that current is the rate of flow of charge


2.15 know and use the relationship between charge, current and time:

charge = current × time

Q = I × t

2.16 know that electric current in solid metallic conductors is a flow of negatively charged electrons

[See 2.14]

2.17 understand why current is conserved at a junction in a circuit

2.18 know that the voltage across two components connected in parallel is the same


2.19 calculate the currents, voltages and resistances of two resistive components

connected in a series circuit

2.20 know that:

• voltage is the energy transferred per unit charge passed

• the volt is a joule per coulomb


2.21 know and use the relationship between energy transferred, charge and voltage:

energy transferred = charge × voltage

E = Q × V

2.22 identify common materials which are electrical conductors or insulators,

including metals and plastics


thequarkyteacher.files.wordpress.com€¦ · Web view2.17. understand why current is conserved at a junction in a circuit. 2.18. ... Key Word. Image. Definition. Charge. The physical

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