4.3.2 Series and parallel circuits (3)
Resources |
Revision Questions |
Physics
Login to see all questions
Click on a question to view the answer
1.
Three resistors are connected in series. Their resistances are 8Ω, 15Ω and 24Ω. Calculate the total resistance of the series combination.
For resistors in series, the total resistance is the sum of the individual resistances.
Rtotal = R1 + R2 + R3
Rtotal = 8Ω + 15Ω + 24Ω = 47Ω
Answer: The total resistance is 47Ω.
2.
A circuit contains a junction where three wires meet. Current I1 flows into the junction, current I2 flows out along one path, and current I3 flows out along another path. State the junction rule and write an equation that represents this rule in terms of the currents.
Junction Rule: The sum of the currents entering a junction in a circuit is equal to the sum of the currents leaving the junction. This is due to the conservation of charge.
Equation: I1 = I2 + I3
3.
Question 3
Two resistors, R1 = 10Ω and R2 = 20Ω, are connected in parallel to a 12V battery. Calculate the p.d. across each resistor.
Concept Used: The p.d. across an arrangement of parallel resistances is the same as the p.d. across one branch in the arrangement of the parallel resistances. The voltage across parallel resistors is the same. We can use Ohm's Law to calculate the current through each resistor and then find the p.d. across each.
Solution:
- Calculate the total resistance: The equivalent resistance (Req) of two resistors in parallel is: 1/Req = 1/R1 + 1/R2 = 1/10Ω + 1/20Ω = 3/20Ω. Therefore, Req = 20/3Ω ≈ 6.67Ω.
- Calculate the total current: The total current (I) flowing from the battery is: I = V/Req = 12V / (20/3Ω) = 12V * (3/20Ω) = 1.8A.
- Calculate the p.d. across R1: The p.d. (V1) across R1 is: V1 = I * R1 = 1.8A * 10Ω = 18V.
- Calculate the p.d. across R2: The p.d. (V2) across R2 is: V2 = I * R2 = 1.8A * 20Ω = 36V.
Answer: The p.d. across R1 is 18V and the p.d. across R2 is 36V.