A technician is testing a filament lamp from a car - Edexcel - GCSE Physics - Question 4 - 2017 - Paper 1
Question 4
A technician is testing a filament lamp from a car.
He connects the lamp to a test circuit with a 1.5 V d.c. power supply.
(i) Complete the sentence by putting a c... show full transcript
Worked Solution & Example Answer:A technician is testing a filament lamp from a car - Edexcel - GCSE Physics - Question 4 - 2017 - Paper 1
Step 1
Complete the sentence by putting a cross (X) in the box next to your answer.
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Answer
The power supply transfers D 1.5 volts per joule. This indicates that the energy supplied for each unit of charge moving through the circuit is 1.5 volts.
Step 2
Add an appropriate meter symbol to the circuit to show how the meter should be connected.
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Answer
To indicate how the meter should be connected, add a symbol for an ammeter in series with the circuit.
Step 3
Calculate the resistance of the filament in the lamp.
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Answer
Using Ohm's law, the resistance (R) can be calculated as follows:
R=IV
Where:
V = 1.5 V (Voltage)
I = 0.18 A (Current)
Plugging in the values:
R=0.18 A1.5 V≈8.33 ohms
Step 4
Calculate the power of the lamp.
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Answer
The power (P) can be calculated using the formula:
P=V×I
Substituting the known values:
V = 12 V (Voltage)
I = 800 mA = 0.8 A
So,
P=12 V×0.8 A=9.6 W
Step 5
Explain why the current is not 400 mA.
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Answer
The expectation of 400 mA in the 6 V circuit is based on a direct proportionality assumption. However, the resistance of the filament has changed when connecting to a lower voltage, as well as the temperature of the filament being lower, which results in fewer collisions in the lattice structure. Consequently, the current does not remain proportional to the voltage, leading the actual current to be different from the expected 400 mA.
