D.C. Circuits

Two cylindrical conductors, X and Y, are made from the same material. The conductors have equal lengths, but Y has a smaller diameter than X.
X and Y are connected in series to a cell.
Which row compares the number of charge carriers per unit time passing through X and through Y and compares the average drift speed of the charge carriers in X and in Y?

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Which circuit symbol does not represent an electric component that is designed to emit sound waves?

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The diagram shows a junction in a circuit where three wires, P, Q and R, meet. The currents in P and Q are $1\text{ A}$ and $3\text{ A}$ respectively, in the directions shown.

How much charge passes a given point in wire R in a time of $5\text{ s}$?

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A   $0.4\text{ C}$
B   $2\text{ C}$
C   $10\text{ C}$
D   $20\text{ C}$

A cell of electromotive force (e.m.f.) $E$ and internal resistance $r$ is connected in series with a switch S and an external resistor of resistance $R$.

The potential difference (p.d.) between P and Q is $V$.
Which statement is correct when S is changed from open to closed?

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A   $V$ increases because there is a p.d. across $R$.
B   $V$ decreases because there is a p.d. across $r$.
C   $V$ remains the same because the decrease of p.d. across $r$ is balanced by the increase of p.d. across $R$.
D   $V$ remains the same because the sum of the p.d.s across $r$ and $R$ is still equal to $E$.

The diagram shows six identical resistors connected in a circuit.

In which branch of the circuit is the most power dissipated?

Options

A   PQ
B   QR
C   RS
D   SP

The diagram shows a circuit containing a thermistor, a fixed resistor and a battery.

The graph shows the $I$–$V$ characteristics of both components.

The battery has an e.m.f. of $12\text{ V}$ and negligible internal resistance.

What is the current in the fixed resistor?

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A   $0.36\text{ mA}$
B   $0.40\text{ mA}$
C   $0.48\text{ mA}$
D   $0.80\text{ mA}$

Two resistors of resistances $R_1$ and $R_2$ are connected in parallel.

What is the combined resistance between X and Y?

Options

A   $R_1 + R_2$
B   $\dfrac{R_1R_2}{R_1 + R_2}$
C   $\dfrac{R_1 + R_2}{R_1R_2}$
D   $\dfrac{R_1}{R_2}$

A cell is connected in series with an ammeter and a variable resistor. A voltmeter is used to measure the p.d. across the variable resistor. The resistance of the variable resistor is varied, and the p.d. and the current are recorded.

The graph shows the variation with current of the p.d. across the variable resistor.

What is the internal resistance of the cell?

Options

A   $0.050\Omega$
B   $1.6\Omega$
C   $20\Omega$
D   $23\Omega$

The diagram shows a cell of internal resistance $1.0R$ connected to a variable resistor.

When the variable resistor has an initial resistance of $2.0R$, the current in the cell is $I_1$ and the terminal potential difference (p.d.) across the cell is $V_1$.

The variable resistor is now adjusted to a new resistance of $4.0R$.

What is the new current in the cell and the new terminal p.d. across the cell?

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The diagram shows a four-terminal box connected to a battery and two ammeters.

The currents in the two ammeters are identical.

Which circuit, within the box, gives this result?

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