Required Practical: Investigating Total Resistance

Question 1

Describe the method for investigating total resistance. (5)

Answer 1

1. Set up the circuit so that the ammeter is in series with the bulb and resistor, and the voltmeter is in parallel with the bulb and resistor.
2. Close the switch momentarily and measure the current and p.d.
3. Place results in a suitable table and calculate the resistance using R= V/I
4. Now add a resistor in series. Repeat steps 2 and 3.
5. Repeat step 2, but add a resistor in parallel rather than series.

Question 2

Describe what happens to the total resistance when you add resistors in series.

Answer 2

When you add resistors in series, the total resistance of the circuit is the sum of resistances of the resistors.

Question 3

Describe what happens to the total resistance when you add resistors in parallel and why. (3)

Answer 3

1. When you add resistors in parallel, the total resistance of the circuit decreases.
2. This is because there are multiple paths for the current.
3. This means that for the same p.d the current from the cell increases.

Question 4

Describe the resistance of resistors in parallel.

Answer 4

The resistance of a parallel circuit is less than the resistance of the resistor with the least resistance (e.g. if there was a 2Ω and a 3Ω resistor in parallel, then the total resistance would be <2Ω