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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

The smallest possible unit of charge

1.6 x 10^-19 C

3

Coloumbs Law

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

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

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

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

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

28

Resistivity (ρ)

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

Resistors in series vs parallel

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+...