Required Practical 3 - Use circuit diagrams to set up and check appropriate circuits to investigate the factors affecting the resistance fo electrical circuits

Question 1

Circuit diagram to calculate resistance for different lengths of wire:

Answer 1

Question 2

Method to calculate resistance in circuit for different lengths of wire:

Answer 2

1. Set up apparatus as shown in circuit diagram above
2. Use a ruler measure 5cm of wire and place crocodile clips at each edge of the 5cm of wire
3. Measure the potential difference across the 5cm of wire using a voltmeter connected in parallel across the 5cm of wire
4. Measure the current of the circuit by connecting an ammeter in series in the circuit
5. Calculate the resistance across the 5cm of wire using the formula R = V/I (use for each length)
6. Repeat the whole experiment increasing the length of the wire in increments of 5cm until 45cm
7. To mitigate the errors ensure temperature of the wire is constant by not keeping circuit connected to power source (cell) when not in use and disconnecting in between readings
8. Plot graph - length of wire on the x-axis and resistance on the y-axis

Question 3

Independent variable when calculating resistance in circuit for different lengths of wire:

Answer 3

length of wire

Question 4

Dependent variable when calculating resistance in circuit for different lengths of wire:

Answer 4

resistance

Question 5

Control variables when calculating resistance in circuit for different lengths of wire:

Answer 5

• temperature of wire + surroundings
• components used

Question 6

Hazard, risk and precautions to taken when calculating the resistance in a circuit for different lengths of wire:

Answer 6

hot wires → getting burnt → don’t touch wires will connected to power source for long period of time and allow to cool down when disconnected before touching

Question 7

Results when calculating resistance in circuit for different lengths of wire:

Answer 7

• resistance of wire is directly proportional to the length
• as straight line goes through the origin

Question 8

What is there when the length of the wire is zero?

Answer 8

• systematic uncertainty → contact with wire → not exactly 0cm
• small resistance - shouldn’t be there
  
  • zero error - a reading on a measuring instrument when the value should be zero
  • systematic error which cannot be reduced by carrying out repeats
• in case of resistance, we need to subtract the zero error from all of our readings
• crocodile clip not exactly at zero
• some resistance caused by contact between crocodile clip and wire
• if the temperature of the wire increases then the resistance will also increase
  
  • use low potential difference - will keep current low reducing any heating in the wire
  • only turn on current when taking a reading - turn off current between readings

Question 9

What would the product of current and resistance equal?

Answer 9

the product of current and resistance would equal a constant

Question 10

How would you spot an anomaly in a set of repeats for one value?

Answer 10

• the precise values show little variation
• the anomaly is further away from the mean than the other values