# Electricity Flashcards

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1
Q

what is kirchoffs first law?

A

at any point in an electrical circuit the sum of currents into that point = sum of currents out of that point

2
Q

what is the mean drift velocity

A

the average velocity of electrons moving through a wire

3
Q

mean drift velocity equation

A
```I=Anev
I = current in conductor
n = number density
e = elementary charge
v = mean drift velocity```
4
Q

what effect does a thinner wire have on the mean drift velocity

A

if current is constant then mean drift velocity has to increase as wire gets thinner

5
Q

what does the ideal ammeter have

A

zero resistance

6
Q

what is EMF

A

electro motive force
describes when work is done on charge carriers
where energy is transferred from other energy forms into electrical energy

7
Q

what is PD

A

potential difference
describes when work is done charge carriers
when energy is transferred from electrical energy into other forms of energy

8
Q

what is ohms law

A

for a metallic conductor kept at a constant temperature, the current in the wire is directly proportional to the potential difference across it

9
Q

what is resistivity

A

an electrical property of a material.

resistance is proportional to length/area. the constant is resistivity

10
Q

equation for resistivity

A

R= pl/A

11
Q

as a material gets hotter what happens to its resistivity

A

as a material gets hotter, the resistivity increases

12
Q

what are semiconductors

A

they have negative temperature coefficients so their resistance drops as thei temperature increases

13
Q

A

semiconductors

14
Q

what is power

A

the rate of energy transfer

15
Q

what is kirchoffs second law

A

the sum of electromotive forces is equal to the sum of pds around a closed loop

16
Q

describe current in a series circuit

A

same in every position

17
Q

describe voltage in a series circuit

A

emf is shared equally among resistors with the same resistance
if resistances are different then the resistor of higher resistance will take a higher proportion of the emf

18
Q

total resistance in a series circuit

A

r1+ r2 +r3 e.t.c

19
Q

describe current in a parallel circuit

A

current is shared between paths according to resistance. the higher the resistance the less current

20
Q

describe voltage in a parallel circuit

A

pd across each branch is equal to emf in power supply

pd is shared between components in the branch

21
Q

total resistance in a parallel circuit

A

1/R = 1/r1 + 1/r2 e.t.c

22
Q

what is the difference between the pd in the circuit and the emf in the power supply

A

difference is lost volts
lost volts = Ir
I = current
r = internal resistance

23
Q

how can you calculate emf

A

emf = terminal pd + lost volts

24
Q

equation to find the force between two point charges

A

kQ1Q2/r^2 where k is a constant

25
Q

other equation to find the force between two point charges

A

F=charge X electric field

26
Q

IV graph for a diode

A

slopes up from around 0 one arm going up

27
Q

IV graph for filament lamp

A

through origin, wavy arm going horizontal

28
Q

equation for power

A

P=IV

29
Q

equation for energy with voltage and current

A

E=VIt

30
Q

what is EMF in terms of lost volts

A

emf=terminal pd + lost volts

31
Q

equation for lost volts

A

lost volts = I X r where r= internal resistance