Electric Circuits

The graph shows how the resistance of a thermistor varies with temperature.

The thermistor is at a temperature of $10\,^\circ\text{C}$ and is connected in series with a fixed resistor of resistance $20\ \Omega$.

What is the combined resistance of both components?

Options

A   $16\ \Omega$
B   $20\ \Omega$
C   $80\ \Omega$
D   $100\ \Omega$

Each of the resistors in the circuit shown has a resistance of $6.0\ \Omega$.

What is the total resistance of the circuit?

Options

A   $2.0\ \Omega$
B   $4.0\ \Omega$
C   $9.0\ \Omega$
D   $18\ \Omega$

A student connects the circuit shown.

The switch S is closed.

What is the reading on the voltmeter?

Options

A   $1.0\ \text{V}$
B   $3.0\ \text{V}$
C   $4.5\ \text{V}$
D   $6.0\ \text{V}$

Two resistors connected in series act as a potential divider as shown.

The resistors have resistances $R_1$ and $R_2$ and the potential differences across them are $V_1$ and $V_2$ respectively.

Which expression is equal to $\frac{V_1}{V_2}$?

Options

A   $\frac{R_1}{R_2}$
B   $\frac{R_2}{R_1}$
C   $\left(\frac{R_1}{R_2}\right)^2$
D   $\left(\frac{R_2}{R_1}\right)^2$

A student connects four circuits using two identical cells, two identical resistors and a motor.

In which circuit does the coil of the motor rotate the fastest?

Options

Which component is used in an electric circuit to detect changes in temperature?

Options

A cardboard tube has two wires, P and Q, connected to its ends. Inside the tube, wire P and wire Q are connected to two resistors.

The potential difference (p.d.) between wire P and wire Q is $9.0\ \text{V}$ and the current in the wires is $0.75\ \text{A}$.

Which combination of resistors is inside the tube?

Options

A   a $0.75\ \Omega$ resistor and a $6.0\ \Omega$ resistor in parallel
B   a $0.75\ \Omega$ resistor and a $6.0\ \Omega$ resistor in series
C   a $20\ \Omega$ resistor and a $30\ \Omega$ resistor in parallel
D   a $20\ \Omega$ resistor and a $30\ \Omega$ resistor in series

A resistor of resistance $R$ is connected to a variable resistor, a voltmeter and a power supply of electromotive force (e.m.f.) $E$.

The resistance of the variable resistor increases from $0$ to $2R$.

What happens to the reading on the voltmeter?

Options

A   It increases from $0$ to $\frac{1}{3}E$.
B   It increases from $0$ to $\frac{1}{2}E$.
C   It increases from $0$ to $\frac{2}{3}E$.
D   It increases from $0$ to $E$.

Which circuit contains a heater and a fuse?

Options

A light-dependent resistor (LDR) is to be used as an input sensor for an intruder alarm circuit.
When there is no light on the LDR, the lamp switches on.

The resistance of the fixed resistor is less than that of the lamp.

Which diagram shows the circuit?

Options