Req Prac 2 Resistance

Question 1

Part 1: investigating how a wire’s resistance depends on its length

Question 2

Outline the basic steps of the practical

Answer 2

1. Set-up circuit
2. Attach resistance wire to metre rule
3. Move the crocodile clip along the wire in increments, taking measurements for voltage and current each time
4. Calculate the resistance for each length

Question 3

What two types of meters are needed in the circuit, and how should they be connected?

Answer 3

1. Voltmeter: Connected in parallel to the resistance wire
2. Ammeter: Connected in series with the resistance wire

Question 4

What equation is used to obtain the resistance from the current and voltage readings?

Answer 4

R=V/I

Question 5

What should the graph of resistance against length look like ?

Answer 5

The two variables are directly proportional so should produce a straight line going through the origin

Question 6

In reality, why might the line produced not pass through the origin ?

Answer 6

There may be a zero error. This may be because it is hard to attach the stationary crocodile clip exactly at the zero end of the metre rule

Question 7

Why should the wire used be thin ?

Answer 7

• For a given material, the thinner the wire, the higher the resistance
• This makes the recorded resistance values large enough to be measured and interpreted

Question 8

Why should a low potential difference be used when carrying out this experiment ?

Answer 8

To prevent the current getting too high and the wire heating up

Question 9

What is the issue if the wire heats up during the experiment ?

Answer 9

Resistance of a wire will increase if the temperature increases, creating an extra variable which will interfere with the results.
Temperature should remain a control variable.

Question 10

Why does resistance increase with temperature ?

Answer 10

The metal ions have more kinetic energy so vibrate more. This causes them to collide more frequently with current-carrying electrons, providing more resistance against the flow of electrons.

Question 11

What safety precautions should be taken when carrying out this experiment ?

Answer 11

• avoid touching the wire since it may be very hot
• keep potential difference values low to avoid overheating