Flashcards in Physics Class 4 Deck (30)

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1

## Electric Charge

###
Unit: C

Symbol: Q or q

Can be positive or negative

2

## Elementary Charge

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The smallest possible unit of charge

1.6 x 10^-19 C

3

## Coloumbs Law

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Fe = K (|Q||q| /r^2)

K = 9 x 10^9 Nxm^2 / C^2

4

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

###
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

5

## Electric Field from a point charge

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Electric field moves away if +, towards if -

Unit: N/C

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

6

## Strength of electric field corresponds to ....

### Density of the electric field

7

## Electric potential vs electric field

###
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

8

## Electric potential

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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

9

## Electric potential from a point charge

### V = K x (q/r)

10

## Electric Potential Energy

### ΔPE = qΔφ = qV

11

## Work done by electric field

### W = -ΔPE

12

## Positive charge wants to accelerate to regions of _____ electric potential

### lower

13

## Negative charge wants to accelerate to regions of _____ electric potential

### higher

14

## Batteries

###
Maintain potential difference

- Is NOT source of charge/enery

+ terminal = higher electric potential

- terminal = lower electric potential

15

## Which direction does current flow from?

### + to -

16

## Which direction do electron flow from?

### - to +

17

## Capacitors

###
Store energy & charge

Formula: C= kEo(A/d)

k = 1 if vaccum or air

k>1 if another insulator

Unit: Farads (F)

18

## Q=CV

###
Charge on capacitor

- if capacitor is attached to battery in a closed circut

19

## Energy stores by capacitor

###
PEcap = 1/2QV

= 1/2CV^2

= Q^2 /2C

20

## Calculating electric field with capacitor

###
E = V/d

- electric field goes from + to -

21

## Dielectrics

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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

22

## Conductor

###
Charges move freely

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

23

## Dielectric breakdown

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

24

## Ohm's Law

### V=IR

25

## Flow rate of charge

###
Formula = I = ΔQ/Δt

Units: Amps = c/s

26

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

### J/s = Watts = Power

27

## Resistance

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How much an OBJECT opposes the charge through it

R = ρ(L/A)

Units: Ω

28

## Resistivity (ρ)

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How much a MATERIAL opposes the flow of charge through it

Units: ρ = Ω x m

29

## One battery + One resistor

###
Voltage of the battery determines voltage across resistor

**Voltage of battery = Voltage of resistor**

30