H212 DC Circuits

Question 1

When 2 or more resistors are connected in series, how do you calculate the effective resistance and why?

Answer 1

Effective resistance is the sum of the resistances, as the electric current has only one possible path to flow. By conservation of charge, the same current flows through each of the resistors.

Reff = R1+R2+R3

Question 2

When 2 or more resistors are connected in parallel, how do you calculate the effective resistance and why?

Answer 2

The potential difference across each resistor that is connected in parallel is the same. Hence, wire junctions a which the current splits up and re-combines where the branches meet again.

1/Reff = 1/R1+1/R2+1/R3

Question 3

Explain the junction law.

Answer 3

Total current flowing into a junction must be equal to the total current flowing out of it.

I1+I2=I3+I4

Question 4

What is a simpler way to calculate the effective resistance of a pair of resistors in parallel?

Answer 4

Reff = product of resistances/sum of resistances

Question 5

What is a simpler way to calculate the effective resistance of identical resistors in parallel?

Answer 5

Reff = R of one resistor/ No. of resistors

Question 6

What is an earth point?

Answer 6

A point arbitrarily assigned as zero potential

Question 7

What is a short circuit?

Answer 7

A path of zero resistance

Question 8

What is the potential divider rule?

Answer 8

V/Vtotal = R/Rtotal

Question 9

What is the formula for potentiometer circuits?

Answer 9

Vtapped/Vtotal = Ltapped/Ltotal = Rtapped/Rtotal

Question 10

What are the requirements when a potentiometer is under balanced conditions?

Answer 10

• Voltage in primary and secondary circuits is equal
• There are no current wires connected to the galvanometer and resistor in the secondary circuit
• Galvanometer shows null deflection (no current)