Investigating Resistance

Question 1

Where must the ammeter be placed?

Answer 1

In series with whatever you’re investigating.

Question 2

Where must the voltmeter be?

Answer 2

In parallel around whatever you’re investigating.

Question 3

Step 1

Answer 3

Attach a crocodile clip to the wire, level with 0cm on the ruler.

Question 4

Step 2

Answer 4

Attach the 2nd crocodile clip on the wire level with 5cm on the ruler adn record the length (5cm)

Question 5

Step 3

Answer 5

Close the switch then record the current through the wire and the pd across it.

Question 6

Step 4

Answer 6

Open the switch then move the 2nd crocodile clip along 5cm on the wire and record the length. Close the switch again and record the pd and current again.

Question 7

Step 5

Answer 7

Repeat this for the wire at lengths 15cm, 20cm, 25cm, 30cm, 35cm and 40cm.

Question 8

Step 6

Answer 8

Use your measurements for current and pd to calculate the resistance for each length of the wire using R = V/I

Question 9

Step 7

Answer 9

Plot a graph of resistance (y axis) against wire length (x axis) and draw a line of best fit.

Question 10

Step 8

Answer 10

The graph should be a straight line showing that resistance is directly proportional to the length of the wire.

Question 11

Why might the graph not show direct proportion?

Answer 11

A systematic error e.g. the first clip isn’t attached at 0 so all he length reading are a bit incorrect

Question 12

What are the independent variables in this experiment?

Answer 12

Length of wire

Question 13

What are the dependant variable in this experiment?

Answer 13

Resistance

Question 14

What are the control variables in this experiment?

Answer 14

pd of power supply, temp of wire

Question 15

I-V characteristics for a component

Answer 15

in series

Question 16

Step A

Answer 16

Set up a series circuit with a resistor a battery and an ammeter. Ensure the circuit is connected with a battery of 4 V, first with one resistor (R1) with the voltmeter connected in parallel and ammeter in series

Question 17

Step B

Answer 17

Close the switch (if there is one) and record the reading on the voltmeter and ammeter.

Question 18

Step C

Answer 18

Repeat steps 1 and 2 for just the second resistor (R2)

Question 19

Step D

Answer 19

Open the switch and add connect both R1 and R2 in series, connecting the voltmeter in parallel to both resistors

Question 20

Step E

Answer 20

Close the switch and record the new readings on the voltmeter and ammeter.

Question 21

Step F

Answer 21

Plot a graph with resistance on the y axis

Question 22

Step G

Answer 22

Open the switch and arrange R1 and R2 now in parallel.

Question 23

Step H

Answer 23

Close the switch and record the readings on the voltmeter and ammeter

Question 24

Step I

Answer 24

Plot a graph with resistance on the y axis

Question 25

What is the independent variable?

Answer 25

Number of resistors

Question 26

What is the dependent variable?

Answer 26

Total resistance, R

Question 27

What is the control variable?

Answer 27

.Pd of power supply
.temp of resistors

Question 28

What do the results show in series?

Answer 28

.the resistance of the combined resistors = the sum of the two individual resistances
.this is cos the electrons flow through just one path through both resistors, so the current does too

Question 29

What do the results show in parallel?

Answer 29

.the resistance of the combined resistors is less than the sum of the two individual resistances
.this is because the electrons are split between the different paths (or ‘loops’) but the resistors still have the same potential difference across them