Physics Class 4

Question 1

Electric Charge

Answer 1

Unit: C
Symbol: Q or q
Can be positive or negative

Question 2

Elementary Charge

Answer 2

The smallest possible unit of charge

1.6 x 10^-19 C

Question 3

Coloumbs Law

Answer 3

Fe = K (|Q||q| /r^2)
K = 9 x 10^9 Nxm^2 / C^2

Question 4

If you know the electric field, you can find the electric force by:

Answer 4

Fe = qE

Because q is scalar, if it is a + direction, Fe is the same direction as E

If it is a - direction, fe is opposite direction as E

Question 5

Electric Field from a point charge

Answer 5

Electric field moves away if +, towards if -
Unit: N/C

Equation: E = k x |Q|/r^2

Question 6

Strength of electric field corresponds to ….

Answer 6

Density of the electric field

Question 7

Electric potential vs electric field

Answer 7

Electric potential is the scalar field created by source charges that permeates space around them

Electric field is vector field created by source charges that permeates space around them

Question 8

Electric potential

Answer 8

Changes in potential energy (similar to changes in height) are needed to calculate changes in electric PE

Unit: V (= J/C = PE/q)
Can be +, -, 0

Question 9

Electric potential from a point charge

Answer 9

V = K x (q/r)

Question 10

Electric Potential Energy

Answer 10

ΔPE = qΔφ = qV

Question 11

Work done by electric field

Answer 11

W = -ΔPE

Question 12

Positive charge wants to accelerate to regions of _____ electric potential

Answer 12

lower

Question 13

Negative charge wants to accelerate to regions of _____ electric potential

Answer 13

higher

Question 14

Batteries

Answer 14

Maintain potential difference
- Is NOT source of charge/enery

+ terminal = higher electric potential
- terminal = lower electric potential

Question 15

Which direction does current flow from?

Answer 15

+ to -

Question 16

Which direction do electron flow from?

Answer 16

• to +

Question 17

Capacitors

Answer 17

Store energy & charge
Formula: C= kEo(A/d)
k = 1 if vaccum or air 
k>1 if another insulator
Unit: Farads (F)

Question 18

Q=CV

Answer 18

Charge on capacitor

- if capacitor is attached to battery in a closed circut

Question 19

Energy stores by capacitor

Answer 19

PEcap = 1/2QV
= 1/2CV^2
= Q^2 /2C

Question 20

Calculating electric field with capacitor

Answer 20

E = V/d

- electric field goes from + to -

Question 21

Dielectrics

Answer 21

Opposite direction of electric field
- makes it more difficult for charges to attract, thus increasing resistance so you can store more charge by increasing capacitance

Question 22

Conductor

Answer 22

Charges move freely

Applying a potential difference (voltage) across a conductor induces a net movement of charge

Question 23

Dielectric breakdown

Answer 23

Insulator is ionized by too large of an external electric field, allowing charges to move through it

Question 24

Ohm’s Law

Answer 24

V=IR

Question 25

Flow rate of charge

Answer 25

Formula = I = ΔQ/Δt

Units: Amps = c/s

Question 26

What does the slop of a V(voltage) x I (current) graph give you?

Answer 26

J/s = Watts = Power

Question 27

Resistance

Answer 27

How much an OBJECT opposes the charge through it
R = ρ(L/A)
Units: Ω

Question 28

Resistivity (ρ)

Answer 28

How much a MATERIAL opposes the flow of charge through it

Units: ρ = Ω x m

Question 29

One battery + One resistor

Answer 29

Voltage of the battery determines voltage across resistor

Voltage of battery = Voltage of resistor

Question 30

Resistors in series vs parallel

Answer 30

Series = same CURRENT
Req = R1 + R2+ R3 ...
Req = V1/i + V2/i + V3/i+...

Parallel = same Voltage
1/Req = 1/R1 + 1/R2 + 1/R3 ...
Req = I1/V + I2/V + I3/V+...