You will complete 12 Specified Practical Activities if you are studying GCSE Physics. You could be asked questions about the apparatus, methods, safety precautions, results, analysis and evaluation of these experiments.
A pupil was asked to investigate which was the best way to connect 20 12 V 0.1 A light bulbs, in series or in parallel, for his Christmas tree decorations.
The 20 bulbs were connected in series to a 12 V power supply and the voltage was measured across one of the bulbs. Then the 20 bulbs were then connected in parallel to the 12 V supply and the voltage was again measured across one of the bulbs.
a) For each case:
i) Predict the value for the voltage. Give a reason for your choice. [2 marks]
ii) Predict what happens when one bulb is removed from its socket. Give a reason for your prediction. [2 marks]
The pupil decides to investigate the parallel circuit further and decides to add more than the 20 bulbs to the circuit. After adding two more bulbs the power supply's 2 A fuse 'blows' and the bulbs all go off.
b) Explain why this has happened. [3 marks]
This question has been written by a Bitesize consultant as a suggestion to the type of question that may appear in an exam paper.
i) 0.6 V (12 ÷ 20)  because the supply voltage is shared in series circuits. 
ii) All the other bulbs will be off , there is a break in the circuit. 
i) 12 V because the same voltage is across each bulb irrespective of the quantity. 
ii) All the other bulbs will remain on at the same brightness as there is more than one path for the current to flow. 
b) Each bulb takes a current of 0.1 A when connected to 12 V . When you have 20 bulbs connected in parallel the total current from the supply will be 20 × 0.1 A = 2 A. The fuse is just able to hold . When you add another two bulbs, the current increases to 2.2 A and the 2 A fuse will 'blow' .
The circuit shown is used to investigate how the resistance depends upon the length of a wire:
The results from the experiment are shown in a table.
|Length of wire (cm)||Voltage (V)||Current (A)||Resistance of wire (Ω)|
a) Recall an equation to find the missing value in the equation. [2 marks]
b) Write down the name of the quantity that is measured by X in the diagram above. [1 mark]
c) Use the table to answer the following question. The science technician stated that a one metre length of the wire had a resistance of 30 Ω. Explain whether this statement was true. [2 marks]
Question courtesy of Eduqas.
b) Current 
c) The resistance of 100 cm would be 20 Ω (30 Ω requires a 150 cm length)  therefore the statement is not true .