Miskonsepsi Dalam Topic Keelectrikan

Miskonsepsi Dalam Topic Keelectrikan

1. Arus elektrik hanya wujud jika ada pergerakan elektron (X)(All electric currents are flows of electrons) (X)

Arus elektrik bukan setakat pengaliran electron tetapi pengaliran cas elektrik (cas negatif, cas positif dan proton) (√ )Electric currents are not just flows of electrons, but are flows of electric charge(negative charge, positive charge and proton) (√ )

(Penggunaan contoh)

Examples of flows positively charge and protons as electric current:Current in a metal wire is a flow of electrons, but in many other conductors both the positive and negative charges can flow. Both protons and electrons posses exactly the same amount of ‘electricity.’ If either the protons *OR* the electrons flow, that flow is an electric current. i). In salt water, in fluorescent bulbs, and in battery acid, atoms with extra protons (positively charged atom) can flow along, and this flow is a genuine electric current. ii). In fuel cell membranes and in solid ice, electric current is actually a flow of protons.

2. Arus bergerak dari terminal negatif ke terminal positive (X)Electric current flow from negative terminal to positive terminal (X)

Arus Konvensional mengalir dari terminal positive ke terminal negatif (√ ) Conventional current flow from positive terminal to negative terminal( √ )

(Penggunaan Contoh)

Contoh arus disebabkan pengaliran cas dalam 2 arah Example of Two-way Positive/Negative electric current

i) During an electric shock, no electrons flow through the victim’s body. The electric current inside our tissues is made of positively charged atoms flowing one way and negatively charged atoms flowing the other. During the electrocution, it was these atoms which flowed along as an electric current. The electric current was a flow of positive sodium and potassium atoms, negative chlorine, and numerous other more complex positive and negative molecules., the positive atoms flowed in one direction, while the negative atoms simultaneously flowed in the other. the flows as being like crowds of of tiny moving dots, with half the dots going in one direction and half in the other. The crowds of little dots move through each other without any dots colliding. The negative atoms behave like electrons which drag an entire atom along with them, while the postive atoms behave like a proton, but a proton with an entire atom attached

ii). Batteries are another example of non-electron or "ionic" conductors. When we connect a light bulb to a battery, we form a complete circuit, and the path of the flowing charge is through the inside of the acid, as well as through the light bulb filament. Battery electrolyte is very conductive. Down inside the battery, within the wet chemicals between the plates, the amperes of flashlight current appears as a flow of both positive and negative atoms. There is a powerful flow of electric

charge going through the acid battery, yet no individual electrons flow through the battery at all. So, while the current is between the two plates of the battery, what's its real direction? Not right to left, not left to right, but in both directions at once. About half of the charge-flow is composed of positive atoms, and the remaining portion is composed of negative atoms flowing backwards. Outside the battery in the metal wires the real particle flow is only from negative to positive. But inside the battery's wet electrolyte, the charge-flow goes in two opposite directions at the same time.

So, in these situation, in which direction did the electric current REALLY go? Do we follow the negative particles and ignore the positive ones? Or vice versa?

In order to simplify our mental picture of Electric Currents, we cut away the unused parts of the picture. We make the negative particles positive, then add their current to any positive particles which were flowing. We stop thinking of current as being a flow of charges. Instead we INTENTIONALLY DEFINE "electric current" as being a flow of exclusively positive particles flowing in one particular direction.

3. Kuantiti arus yang melalui perintang yang berbeza dalam litar sesiri adalah berbeza (X)Quantity of current flowing through different resisitors connected in series is different (X)Kuantirti arus yang melalui perintang yang berbeza dalam litar sesiri adalah sama (√ )Quantity of current flowing through different resistors connected in series is the same (√ )

(Penggunaan Analogi) Current - Water Flow rate Analogy

Volume flow rate in liters/min, cm3/sec, m3/sec, etc.

Electric current flow in coulombs/sec = amperes.

A large pipe offers very little resistance to flow, as shown

by Poiseuille's law.

A wire offers very little resistance to charge flow according to Ohm's law.

Connecting a battery to an appliance through a wire is like using a pipe for water flow.

It's a common misconception that charges slow down as they go through the filament of a bulb because the filament is thinner than the wires in the rest of the circuit. The current is the same even if the wires have different thicknesses because the speed of the charges changes.

When road traffic goes through a bottleneck it slows down.  But with charges the opposite happens.  This is because the current has to stay constant.  In other words the number of

charges passing a point each second has to stay constant.  If fewer charges can go side-by-side then they have to go quicker.

Different resistors is analogy to the different size of the water pipe. Under steady condition, a certain amount water molecule enter any part of the pipe is equavalent to the same amount of water molecule leaving the pipe

Flow rate (Current ) in a parallel circuit

Flow rate (Current ) in a series circuit

4. Dalam satu litar selari, beza keupayaan merentasi setiap komponen adalah berbeza (X)In a parallel circuit, the potencial drop across each component in the circuit is differentDalam satu litar selari, beza keupayaan merentasi setiap komponen adalah sama (√ )In a parallel circuit, the potencial drop across each component in the circuit is the same (√)

(Penggunaan Analogi)

Voltage-Water Pressure Analogy

A battery is analogous to a pump in a water circuit. A pump takes in water at low pressure and does work on it, ejecting it at high pressure. A battery takes in charge at low voltage,

does work on it and ejects it at high voltage. Potential Difference/Voltage Drop is analogy to Pressure difference/Pressure Drop)

V1=V2= 3V

5. Arus elektrik pada perintang yang berbeza rintangan, dalam 1 litar selari adalah sama (X)Current following through resistors of different resistance in a parallel circuit is the same (X)Arus elektrik pada perintang yang berbeza rintangan, dalam 1 litar selari adalah tidak sama (√)Current following through resistors of different resistance in a parallel circuit is different (√)

(tube/resistor)

Long tubes (pressure/voltage probes)

Long tubes (pressure/voltage probes)

From pump

To reservoir

(tube/resistor)

(Penggunaan Analogi)

Resistor with less resistance can be wire with more free electron or thick wireIf the amount free electron flow through a particular point is higher, then the current flowing is also higher.

Thick wires have a lower resistance because the charges have more space (X)

If charges move through empty wires then it makes sense that the charges must move quicker when the wire is wider because there's more space. This isn't what happens.  The wire is already full of charges no matter how thick it is.  The lattice of positive ions completely fills the wire because that's what the wire is made from.  Having a thicker wire doesn't create more gaps. In a given metal the speed of the charges depends only on the voltage.  We can model a thick wire as lots of thin wires side by side.  The current is bigger because each wire contributes charges passing a point each second. 

An analogy is a three-lane road with the cars travelling at 30 mph has more cars passing a tree each second than a single-carriageway road with the cars travelling at the same speed.

If the amount of charges passing through a particular point is higher, then the current flowing is also higher.

Contoh lain analogi yang boleh digunakan

I2 ≠ I3

I = I1= I2+I3=I4

Analog Targetwater -- electricitywater flow -- electric currentpipe -- wirecurled pipe -- resistancepump -- dry celltap -- electric switch

Analog Targetwater -- electricityWater level difference -- Potential differencewater flow -- electric currentglass pipe -- conductor wireat the same level water in pipe -- same potential difference between two pole of the cell

In this analogy, the current shared two wires is imitated water in a riverseparated two branch. Here the electric current is imitated flowingwater in the river

Kajian Tindakan Fizik Tingkatan 5, Tahun 2009Tajuk :- Penggunaan Contoh dan Analogi Untuk Menyelesaikan Masalah Miskonsepsi

Dalam Tajuk Kelektrikan.(Soalan Ujian Pra & Ujian Pos)

1. In the figure below draw the direction of the flow of current with

2. In salt water, fluorescent bulbs, and battery acid, atoms with extra protons can flow along, and this flow is a genuine electric current.

True [ ] False [ ]

3. As you can see on Fig. below, if you make a circuit and close the switch, electric current flows and turns the light bulb on. Current is the flow of [ ].(A) material inside the battery (B) nuclei (C) electric wire (D) electricity (E) electrons

4. The difference in potential causes an …………………….. to flow from one point of higher potential to the point of lower potential.

5. This circuit consists of two bulbs and a variable resistor, R. Both bulbs are lit.

a) The resistance of R is increased.What will happen to the brightness What will happen to the brightnessof bulb 1? of bulb 2?Tick ONE box [ ] Tick ONE box [ ]

It will get brighter [ ] It will get brighter [ ]It will stay the same [ ] It will stay the same [ ]It will get dimmer [ ] It will get dimmer [ ]

b) Tick ONE box [ ] below to explain your reason for choosing these answers.

Increasing R makes the current smaller all round the circuit. [ ]Increasing R makes the current smaller after it. It has no effect on a bulb before it. [ ]Increasing R makes the current smaller after it. So the current before it gets bigger. [ ]The battery always supplies the same current to the circuit. [ ]

LAMPIRAN B

6. In Figure below electric current flowing through point `a' is 3 A (ampere) and through `b' is 2 A. Then what is the electric current flowing through point `c'? (Circle the correct answer)

(A) 1 A (B) 2 A (C) 3 A (D) 5 A (E) 8 A

7. During an electric shock, electrons flow through the victim’s body. These electrons which flowed along as an electric current. True [ ] False [ ]

8. Figure below shows two resistors of 2Ω and 3Ω each which are connected parallel to a cell. Which one of the following is correct (Circle the correct answer)

(A) Voltage drop across 2 Ω resistor =Voltage drop across 3 Ω resistor(B) Voltage drop across 2 Ω resistor >Voltage drop across 3 Ω resistor(C) Voltage drop across 2 Ω resistor<Voltage drop across 3 Ω resistor

9. Which of the following correctly explains the relationships among electric current, voltage, and resistance? (Circle the correct answer)

(A) Electric current is increased when resistance is reduced.(B) Voltage decreases when electric current is increased.(C) Resistance is reduced when voltage is increased.(D) Increase in resistance causes increase in the electric current.(E) Electric current, voltage, and resistance have no relationship to each other.

10. In the figure below, I1 is the current supplied by a source. I2 and I3 are the current in each branch of the parallel arrangements shown.

Which of the following statements concerning I1 I2 and I3 is correct? (Circle the correct answer)(A) I1 is equal to I2 but bigger than I3

(B) I2 is bigger than I3 but smaller than I1

(C) I2 is equal to I3 but smaller than I1

(D) I3 is bigger than I2 but smaller than I1