Name two ways that the electromagnetic force and gravitational force are different.
Jan 21, 2016
Name two ways that the electromagnetic force and gravitational force are different.
Notes on Electric PotentialElectric Field Imagine we have the Earth and a large
asteroid as shown below.
What will happen to the asteroid? Why?
notes
Notes on Electric PotentialElectric Field Imagine we have the Earth and a large
asteroid as shown below.
What will happen to the asteroid? Why?
It will be drawn toward
the Earth and impact it
from Earth’s gravitational field.
notes
Notes on Electric PotentialElectric Field Now imagine we have the charges shown
below.
1C
-1,000 C
What will happen to the + charge? Why?
Notes on Electric PotentialElectric Field Now imagine we have the charges shown
below.
1C
-1,000 C
What will happen to the + charge? Why?
It will get pulled to the
negative charge
because of their electric field.
Notes on Electric PotentialField Lines So how do we draw this? The type of
charge matters, so we need some way of showing direction and strength. We do this with field lines.
Notes on Electric PotentialField Lines So how do we draw this? The type of
charge matters, so we need some way of showing direction and strength. We do this with field lines.
Scientists decided a long time ago that lines should go out from positive and in to negative.
The vectors always point in the direction of the force that would act on a small positive test charge placed in the field
Notes on Electric PotentialField Lines There are 3 things we need to know about
field lines:
1) + charges move in the direction of the arrow, - charges move backwards.
2) The more closely packed the arrows are, the stronger the electric field is.
3) Unlike gravity, electric field lines can be blocked.
Notes on Electric PotentialElectric Shielding
Metal and conductors shield or change our field lines. This is because electrons in metal can move very easily. Since they can move very easily, they try to spread out into the best configuration possible.
Notes on Electric PotentialElectric Shielding
Metal and conductors shield or change our field lines. This is because electrons in metal can move very easily. Since they can move very easily, they try to spread out into the best configuration possible.
Example: a charged, hollow sphere
The charge spreads evenly, no matter where we place the charge inside!
– –
–
–
– – – –
–
–
–
– –
– –
– – – –
+
Notes on Electric PotentialElectric Shielding
Example: a charged, hollow cube
The charge spreads out to get close to the positive, bu away from other negatives. This causes more to cluster on corners.
–
–
– – – – – – – – –
–
–
–
– – – – – – –
+
Notes on Electric PotentialElectric Shielding
Faraday Cage
Example: a charged, hollow cube
The charge spreads out to get close to the positive, bu away from other negatives. This causes more to cluster on corners.
If we put charges inside a box like this, we can tell how intense the charge is, but not where it's located since it evens out. Places like the FBI make use of this a lot.
–
–
– – – – – – – – –
–
–
–
– – – – – – –
+
Notes on Electric PotentialElectric Potential
Just like how we have gravitational potential energy, we can have electric potential energy.
Think of it like gravity.
Positive charge wants to flow “downhill”. Negative charge wants to flow “uphill”.
Notes on Electric PotentialElectric Potential
Assuming same charges, the farther we get from a charge, the less potential we have. We can draw lines of equipotential around charges. These are like elevation on a map. Charges can move on an equipotential line without using energy!
e-field lines
High potential
equipotential
Low potential circles
Notes on Electric PotentialElectric Potential
Electric Potential formula
move charges around
Notes on Electric PotentialElectric Potential
Electric Potential formula
move charges around
Change in voltage
work done=
___________
charge
Work (J)Charge (C)Voltage (V)
Equations
Equations Electric Field Strength
equations
mor V
Vocabulary Electric Field
Field Lines
Conductor
Equipotential
Electric Potential
Volt
The field created by charges that affects all other charges nearby.
A way of showing what the electric field looks like around a charge.
An object that has free-flowing electrons. These can also shield electrical fields.
Places or curves in an electric field that have the same electric potential energy.
The energy a charge can gain or lose by flowing “uphill” or “downhill” along field lines.
How much energy can be loaded on each Coulomb of charge.
vocab
Exit Question #6
Which way do electric field lines and potential lines run?
a) Both go from + to -
b) Both go around a charge
c) Potential goes from + to -, field lines go around a charge
d) Potential goes from - to +, field lines go around a charge
e) Field lines go from + to -, potential go around a charge
f) Field lines go from - to +, potential go around a charge