electricity - required practicals

Question 1

3a: resistance in a wire
what is the aim

Answer 1

to investigate how the resistance of a wire changes with its length

Question 2

3a: resistance in a wire
equipment

Answer 2

• length of constantan wire attached to a metre ruler
• ammeter
• voltmeter
• power supply
• connecting leads with a jockey (a metal terminal with a fine point that can be placed on the test wire) on one end

Question 3

3a: resistance in a wire
method

Answer 3

• set up the circuit:
  > connect one terminal on the power supply to the ammeter, then from the ammeter to the end of the test wire (at 0) and connect the jockey to the power supply
  > connect the voltmeter to the circuit - one lead is connected to the fixed end of the test wire and the other lead is connected to the jockey
• place the jockey on the test wire at the 10cm mark - take readings from the ammeter and voltmeter (repeat this 3 times)
• repeat the previous step, moving the jocey along 10cm each time up to 100cm

Question 4

3a: resistance in a wire
results

Answer 4

• record data in a result table with 4 columns - you will need to calculate the resistance by dividing voltage by current
  |length|voltage|current|resistance|
• plot a graph of resistance (y-axis) against length (x-axis) and draw line of best fit

Question 5

3a: resistance in a wire
conclusion

Answer 5

• as the length increases, the resistance increases
• the resistance of a wire is directly proportional to its length
• resistance of a wire is inversely proportional to its cross-section
• metals that are good conductors have lower densities

Question 6

3b: resistors in series and parallel
what is the aim

Answer 6

to investigate how the placement of the resistance affects the overall resistance of the combination

Question 7

3b: resistors in series and parallel
equipment

Answer 7

• locktronics kits
  > base
  > connectors
  > resistors

Question 8

3b: resistors in series and parallel
method

Answer 8

ensure you fit components properly for good electrical connections
use connecting leads to connect meters into your circuit

method 1 - using a single cell to power the circuit, an ammeter, and a voltmeter

• connect the cell and ammeter in series using leads then connect them to the leads either side of the first/last resistors
• connect the voltmeter in parallel across all resistors
• take current and PD readings, then calculate resistance for the combination using V = IR

method 2 - use a mulitmeter set to measure resistance

• no cells needed since the meter provides the power to the circuit
• connect meter either side of the first/last resistor
• resistance can be read directly from the meter

build eight circuits as follows
- 2, 3, 4, 5 identical resistors in series
- 2, 3, 4, 5, identical resistors in parallel

Question 9

3b: resistors in series and parallel
results

Answer 9

for each circuit, measure the overall resistance for the combination of resistors, presenting them in an appropriate manner

Question 10

3b: resistors in series and parallel
conclusion

Answer 10

total resistance of the circuit when the resistors are in parallel if half the original resistance of each resistor
–> when we add resistors in parallel, the resistance decreases (since the current has a choice of route)

total resistance of the circuit when the resistors are in series is the sum of the original resistance of each resistor
–> when we add resistors in series, the resistance increases