iGCSE Physics (0625) 4.3.3 Action and use of circuit components -Exam Style Questions Paper 1 - New Syllabus
▶️ Answer/Explanation
Detailed solution:
As the thermistor is heated, its resistance R th decreases because it is an NTC (negative temperature coefficient) component. Since the components are in series, the total circuit resistance R total =R+R th decreases, which causes the circuit current I to increase according to I= R total V supply , leading to a higher ammeter reading. The voltmeter is connected across the fixed resistor R; as the current I increases, the potential difference across it, V=I×R, must also increase. Consequently, both the ammeter and voltmeter readings increase, making option D the correct choice.
▶️ Answer/Explanation
Detailed solution:
When an electrical appliance has a metal outer casing (a conductor), it must be earthed so that if a fault occurs and a live wire touches the casing, the current flows safely to the ground rather than through a person.
This makes statement 1 correct and statement 2 incorrect.
Conversely, if the outer casing is made of an insulator, such as plastic, it is known as “double insulation.”
Because insulators do not conduct electricity, there is no risk of the casing becoming live, so an earth wire is not required for safety.
Therefore, statement 4 is correct and statement 3 is incorrect, making the combination of 1 and 4 the right choice.
▶️ Answer/Explanation
Detailed solution:
A thermistor is a type of resistor whose resistance depends significantly on temperature, making it useful in temperature-sensing circuits.
Options A, B, and C all describe functions that rely on detecting or responding to changes in temperature.
Option D requires a response to sound, which is not a function of a thermistor; a sound sensor (like a microphone) would be needed instead.
Therefore, a thermistor would not be useful in a circuit designed to activate upon sound detection.