electricity

Question 1

define current

Answer 1

the change in charge per second/ rate of change of charge

Question 2

give the formula for current using charge

Answer 2

I = change in Q/ change in t

Question 3

define voltage

Answer 3

the work done in moving 1 coulomb of charge

Question 4

give the formula for voltage using work done

Answer 4

V = W/Q

Question 5

what is ohm’s law formula

Answer 5

V = IR

Question 6

what is represented by the gradient on an IV graph

Answer 6

the resistance

Question 7

what is the formula for Rt in series

Answer 7

R1 + R2…

Question 8

what is the formula for Rt in parallel

Answer 8

1/R1 + 1/R2 = 1/Rt

Question 9

what does adding resistors in a parallel circuit do?

Answer 9

decrease the total resistance

Question 10

if 2 resistors are in parallel and are of the same value of R, what is Rt

Answer 10

half R

Question 11

experimental description for the IV curve of a bulb

Answer 11

the graph is a cubic curve and therefore resistance isn’t the gradient anymore, at any point the gradient is just voltage/current at that point. as the voltage increases, the current will also increase, there will then be an increase in the temperature of the filament due to an increase in the number of collisions between electrons and filament ions, which in turn will increase the total resistance.

Question 12

reverse bias diode explanation

Answer 12

• diodes only allow current flow one way
• reverse bias is when a diode is facing the opposite way and thus you get negative voltages
  
  • there will be no current flow with a very low current value
  • resistance will be very high

Question 13

diode breakdown

Answer 13

reverse bias above the breakdown value (usually about 50V), this will cause there to be a large current and a 0 resistance.

Question 14

forward bias diode explanation

Answer 14

A positive voltage above the threshold voltage (around 0.6V) will cause a large current flow with very low resistance.
However, a positive voltage below the threshold will cause no current flow with large resistance.

Question 15

what is the formula for resistivity

Answer 15

rho = RA/L

Question 16

what does A represent in the formula for resistivity?

Answer 16

Cross-Sectional Area

Question 17

How do you calculate the CSA of a wire?

Answer 17

pi x radius^2 / 4

Question 18

the gradient of a resistivity graph is what?

Answer 18

rho/A

Question 19

Bullet point the experimental description for resistivity

Answer 19

• record the diameter for the wire using a micrometer in 3 places along the wire to calculate an average.
• measure the length of the wire using a ruler
• measure the resistance of the wire using an ohmmeter
• repeat the readings for 7 lengths of wire
• plot a resistance/length graph
• take the gradient
• calculate the CSA
• use resistivity = gradient x CSA

Question 20

what happens when more light falls upon an LDR

Answer 20

the resistance will decrease

Question 21

what happens as the temperature of a thermistor increases

Answer 21

the resistance will decrease

Question 22

ammeters have

Answer 22

very low voltage

Question 23

voltmeters have

Answer 23

infinite reistance

Question 24

potential dividers for 1 resistor equation is

Answer 24

V/Vt = R/Rt

Question 25

potential dividers equation across a resistor is

Answer 25

Vout/Vin = Rout/Rt

Question 26

what is EMF

Answer 26

electromotive force

Question 27

EMF formula (1) is

Answer 27

EMF = E/Q

Question 28

EMF formula (2) is

Answer 28

EMF = I(R+r)

Question 29

EMF lost volts formula

Answer 29

EMF = Circuit resistace + lost volts(Ir)

Question 30

define power

Answer 30

power is the energy transferred in 1s or the rate of change of energy.

Question 31

Unusual power formula

Answer 31

P =E/t

Question 32

what happens when the temperature of a superconductor drops

Answer 32

the resistance will drop until it eventually drops to 0.

Question 33

where do superconductors drop to 0 resistance

Answer 33

below the critical temperature of that superconductor