The diagram shows an electrical circuit containing a light-dependent resistor (LDR).
What is the circuit diagram for this circuit?
Correct Answer: \( \boxed{\mathrm{A}} \)
The circuit contains an LDR, a potentiometer used as a variable resistor, and an ammeter connected in series with the LDR.
Only circuit (A) correctly shows these components connected as in the photograph.
Therefore, the correct answer is (A).
The diagram shows a circuit with a battery of electromotive force (e.m.f.) \(60\,\mathrm{V}\) and negligible internal resistance, a \(20\,\mathrm{k\Omega}\) resistor, a thermistor and a voltmeter. The resistance of the thermistor is \(20\,\mathrm{k\Omega}\).
The temperature of the thermistor decreases, and this causes its resistance to change by \(50\%\).
After this change, what is the reading on the voltmeter?
Correct Answer: \( \boxed{\mathrm{B}} \)
A thermistor has a negative temperature coefficient, so when its temperature decreases, its resistance increases by \(50\%\) to \(30\,\mathrm{k\Omega}\).
The voltmeter is across the \(20\,\mathrm{k\Omega}\) resistor.
Using the potential divider equation,
\(V=60\times\dfrac{20}{20+30}=24\,\mathrm{V}\).
Therefore, the correct answer is (B).
A potentiometer circuit is used to determine the electromotive force (e.m.f.) \(E_x\) of a cell. The circuit includes a second cell of known e.m.f. \(E_0\) and negligible internal resistance, and a uniform resistance wire \(PQ\) of known length.
\(E_x\) is less than \(E_0\).
The movable connection \(J\) can be positioned anywhere along the length of the resistance wire.
Which circuit is suitable for determining \(E_x\)?
Correct Answer: \( \boxed{\mathrm{D}} \)
The known cell \(E_0\) provides the potential gradient along the uniform wire.
The unknown cell \(E_x\) and galvanometer must be connected so that a null point can be found by moving the contact \(J\).
Only circuit (D) has the correct arrangement for potentiometer operation.
Therefore, the correct answer is (D).
