Question
A cell of negligible internal resistance is connected in series with a thermistor, a fixed resistor and an ammeter.
The thermistor is placed in a beaker of water and the temperature of the water is slowly increased.
A graph of current I against the temperature T of the thermistor is plotted.
Which graph could show the variation of I with T?
▶️Answer/Explanation
Ans: B
Question
A wire has a length of 3.0 m and is made of metal of resistivity 4.9 × $10^{-7}\Omega m$.
A potential difference (p.d.) of 12V is applied across the wire so that it has a current of 1.4A.
What is the cross-sectional area of the wire?
(A) 1.2 × $10^{-7}m^{2}$
(B) 1.7 × $10^{-7}m^{2}$
(C) 1.1 × $10^{-6}m^{2}$
(D) 1.3 × $10^{-6}m^{2}$
▶️Answer/Explanation
Ans: B
Question
A car has sensors for detecting the light intensity and temperature of its environment.
The sensors make use of a light-dependent resistor (LDR) and a thermistor.
The car moves from a warm and dark environment into a cold and bright environment.
What are the changes to the resistances of the LDR and thermistor?
▶️Answer/Explanation
Ans: C
Question
An electrical cable is made up of one thick strand of copper wire that is surrounded by eight thin
strands of copper wire. All nine strands of wire are connected in parallel with each other.
A cross-section of the cable is shown.
Each thin strand of wire has cross-sectional area A and length L.
The thick strand of wire has cross-sectional area 4A and length L.
The cable has total resistance R.
Which expression gives the resistivity of copper?
(A) $\frac{4A}{33RL}$
(B) $\frac{12A}{RL}$
(C) $\frac{4AR}{L}$
(D) $\frac{12AR}{L}$
▶️Answer/Explanation
Ans: D