Resistors in series and parallel

Question 1

what is the equation used to calculate resistance?

Answer 1

R = V/I
Resistance = p.d/current
Ω = V/A

Question 2

we have a potential difference of 5V and a resistance of 100 Ω
calculate the current flow

Answer 2

R= V/I
Ω= V/A
rearrange:
i = V/R

current = 5V/100Ω
0.05A

Question 3

2 resistors are in series in a circuit
calculate the current when the potential difference is 20V of both resistors and the resistance of first resistor is 100Ω when and the resistance of second resistor is 50Ω

Answer 3

0.13A

R=V/I
Ω=V/A
current=V/R
current= 20V/150Ω
0.13A

Question 4

a circuit has 3 resistors in series
resistor A has a resistance of 20Ω
resistor B has a resistance of 15Ω
Resistor C has a resistance of 10Ω
the total potential difference of the 3 resistors is 10V
determine the current in the circuit

Answer 4

0.22A
R=V/I
I= V/R
current=10V/45Ω
current =0.22A
(to 2d.p)

Question 5

A current of 0.5A flows through the circuit
2 resistors are in series
the resistance of the resistors is 200Ω and 75Ω
calculate the potential difference across the resistors

Answer 5

137.5A
R=V/I
V=RxI
potential difference = 275Ω x 0.5A
potential difference = 137.5V

Question 6

in resistance in parallel what are we not expected to do in an exam?

Answer 6

calculate the total value from resistors in parallel

Question 7

the total resistance of two resistors in parallel is what?

Answer 7

is less than the resistance of the smallest individual resistor

Question 8

2 resistors are in parallel, one resistor has 150 Ω and the other has 200 Ω
explain the total resistance of these

Answer 8

less than 150 Ω
the total resistance of the 2 resistors in parallel will be less than the resistance of the smallest individual resistor ( less than 150 ohms )

Question 9

why is the total resistance of 2 resistors in parallel less than the resistance of the smallest individual resistor?

Answer 9

with 2 resistors in parallel,

there are 2 pathways for the current to take

more total current will flow through the circuit
if the current has increased but the p.d hasn’t changed, then the total resistance must have decreased.

Question 10

if the current has increased and the p.d hasn’t changed, what does this mean for the total resistance ?

Answer 10

the total resistance must have decreased