Electricity 3

Question 1

what is Kirchhoff’s second law

Answer 1

the sum of e.m.fs in a closed loop = the sum of p.ds in a closed loop

Question 2

what is the equation for resistors in series

Answer 2

Rt = R1 + R2 + R3…

Question 3

what is the equation for resistors in parallel

Answer 3

1/Rt = 1/R1 + 1/R2 + 1/R3

Question 4

what are lost volts and what causes them

Answer 4

the lost volts are an amount of e.m.f that does not go to the circuit, because of internal resistance in the cell due to the cell parts themselves dissipating energy

Question 5

what is the terminal p.d

Answer 5

the p.d of the entire rest of the circuit (not the cell and its internal p.d)

Question 6

what are the e.m.f equations

Answer 6

e=V+Ir e=I(R+r)

Question 7

what is a potential divider, why are they useful

Answer 7

it splits up a potential difference as the

Question 8

what is a potential divider, why are they useful

Answer 8

it splits up a potential difference as the component or appliance may need a smaller potential difference than is provided, e.g a phone charger will not need the 230V mains

Question 9

how can LDRs and thermistors be used in potential divider circuits

Answer 9

• LDRs can be used to make lights that turn on when it is dark, and off when it is light
• thermistors can be used to make an oven heat up when it falls below a certain temperature, and stop heating when it reaches a certain temperature

Question 10

what is the rule for potential dividers

Answer 10

the ratio of voltages = the ratio of resistances

V1/V2 = R1/R2