Electricity and Magnetism

Which of these objects would be attracted to a magnet?

Why does an iron nail get attracted to either pole of a magnet?

Which of the following describes the magnetic field lines around a single bar magnet?

How do you identify a 'neutral point' in a magnetic field?

In a solenoid, the magnetic field is most uniform and strongest:

Which of the following would be the best choice for making the needle of a navigational compass?

If an iron bar is placed near a strong magnet but not touching it, what is the process called that makes the iron bar act like a magnet?

If the magnetic field lines are exiting a surface, that surface is acting as a:

Which of the following is an example of a temporary magnet?

A compass needle is free to rotate in both horizontal and vertical planes. Where on Earth will the needle stand perfectly horizontal?

Which of the following is equivalent to one Watt?

Which equation relates energy $E$, potential difference $V$, and charge $Q$?

A device uses $1200\text{ J}$ of energy in $1\text{ minute}$. What is its power rating?

What happens to the resistance of a filament lamp as the current through it increases?

In the series circuit shown in the diagram, a battery provides an electromotive force (e.m.f.) of $12\text{ V}$. A voltmeter is connected in parallel with a $40\text{ }\Omega$ resistor and measures a potential difference of $8.0\text{ V}$. What is the resistance of resistor $R$?

A $12\text{ V}$ battery supplies a current of $2\text{ A}$ for $10\text{ s}$. How much energy is supplied by the battery?

An LDR is placed in a dark room. As the room gets brighter, the current in a series circuit containing the LDR and a battery will:

The resistance of a filament lamp is measured at different voltages. Why does the resistance increase as the voltage increases?

A current of $0.5\text{A}$ flows through a $12\Omega$ resistor for $2$ minutes. How much heat energy is produced?

Two resistors are connected in series. The p.d. across the $10\Omega$ resistor is $4\text{V}$ and the p.d. across the other resistor is $6\text{V}$. What is the resistance of the second resistor?

In the circuit shown, three identical resistors, each with resistance $R$, are connected to a cell of electromotive force (e.m.f.) $V$ and negligible internal resistance. What is the total equivalent resistance of the circuit?

An ammeter is used to measure current in a circuit. How should it be connected relative to the component?

In the circuit shown, if one lamp blows (fails open), what happens to the other lamp?

What is the total resistance of two $10\,\Omega$ resistors connected in series?

In the circuit shown, the ideal voltmeter reads $4\,V$. What is the resistance of $R$?

If the power dissipated in the $6\,\Omega$ resistor is $24\,W$, what is the potential difference across it?

In the bridge circuit shown, if the galvanometer $G$ reads zero, what is the value of $X$?

A research engineer is designing a heating system for a small environmental chamber. The circuit consists of a dc power supply with an electromotive force (e.m.f.) of $12.0\text{ V}$ and an internal resistance of $1.50\,\Omega$. This is connected to a network of three identical heating resistors, each with a resistance of $R = 6.00\,\Omega$. Two resistors are connected in parallel with each other, and this combination is connected in series with the third resistor and the power supply. Calculate the potential difference across the parallel combination of resistors.

A student connects a battery of electromotive force (e.m.f.) $E$ and internal resistance $r$ to a variable resistor $R$. The student measures the terminal potential difference $V$ for different values of current $I$. If the student then connects an identical second battery in parallel with the first, how does the slope and the y-intercept of the $V$ vs $I$ graph change compared to a single battery?

In a bridge-like measurement circuit, four resistors are arranged in a loop. $R_1 = 100\,\Omega$, $R_2 = 200\,\Omega$, and $R_3 = 300\,\Omega$ are fixed. $R_x$ is an unknown resistor. A sensitive galvanometer is connected between nodes B and D. If the galvanometer reads zero current (the bridge is balanced) when $R_x$ is connected, what is the equivalent resistance of the entire network as seen by the $10\text{ V}$ battery connected across nodes A and C?

In a standard UK mains circuit, a fuse is a critical safety component. Which statement correctly describes the function and placement of a fuse in a domestic appliance circuit?

What is the primary function of an earth wire in a domestic appliance with a metal casing?

If a circuit breaker is labeled '$16\text{ A}$', what does this value represent?

What happens to the resistance of a human body when the skin is wet compared to when it is dry?

A student investigates the safety of a faulty electric heater. The heater has a power rating of $2.3\text{ kW}$ and operates on a $230\text{ V}$ mains supply. If an internal fault causes the live wire to touch the metal case, which is connected to the earth wire (resistance $R_e = 0.5\text{ }\Omega$), what is the most appropriate fuse rating to ensure the circuit breaks immediately?

In a domestic ring main circuit, multiple sockets are connected in parallel. What is a primary advantage of using a ring main over a single radial circuit for power distribution?

A Residual Current Device (RCD) is used for safety. On what principle does an RCD operate to detect a fault?

An industrial technician is troubleshooting a faulty electric kiln connected to a $230\text{ V}_{\text{rms}}$ AC mains supply. The kiln is protected by a $13\text{ A}$ fuse and an Earth Leakage Circuit Breaker (ELCB). During a cycle, a high-resistance fault develops where the live heating element touches the metal casing, creating a fault path to earth with a resistance of $R_f = 460\text{ }\Omega$. If the human body resistance is estimated at $1.5\text{ k}\Omega$ and a person touches the casing during this fault, which statement correctly describes the safety outcome before the system is manually isolated?

A technician connects a sensitive oscilloscope to a circuit powered by a 230 V mains supply. The oscilloscope's metal chassis is earthed. Due to a wiring error in the laboratory, the Neutral and Earth connections in the wall socket have been swapped. When the technician connects the oscilloscope's ground clip to the 'Neutral' rail of the circuit under test, what happens?

An electrician is testing the continuity of the earth bond in a commercial kitchen. The potential difference between the metal frame of a refrigerator and the 'true earth' is measured while a small leakage current of 2.0 A is simulated. If the resistance of the earth wire ($R_e$) is found to be $0.8 \Omega$, calculate the 'touch voltage' ($V_t$) and determine if the setup meets safety standards which usually require $V_t < 50 \text{ V}$.

What is the role of an electric relay?

When using the right-hand grip rule for a solenoid, what does the thumb point towards?

A step-up transformer has $50$ turns on the primary and $500$ turns on the secondary. If the primary voltage is $20V$, what is the secondary voltage?

How can the direction of rotation of a DC motor be reversed?

When a wire moves through a magnetic field, the induced current creates its own magnetic field. What is the direction of this new magnetic field?

Which of the following would produce a larger deflection on a galvanometer when a magnet is moved into a coil?

In a transformer, if the input power is $400\text{ W}$ and the output power is $380\text{ W}$, what is the efficiency?

A transformer is used to provide $12\text{ V}$ to a $36\text{ W}$ lamp from a $240\text{ V}$ mains supply. If the transformer is $90\%$ efficient, what is the current drawn from the mains?

A proton enters a uniform magnetic field at right angles to the field lines. What is the shape of its path and does its speed change?

Two coils are wound on the same iron core. Coil 1 is connected to a power supply and a switch. Coil 2 is connected to a lamp. Which action will cause the lamp to light up continuously?

A transformer has an input power of $50W$. If the secondary current is $2A$ and the secondary voltage is $20V$, what is the efficiency of the transformer?

If the primary voltage is $V_p$ and the secondary voltage is $V_s$, and $V_s > V_p$, which must be true?

What happens if the core of a transformer is replaced with a plastic core?

A transformer is used to charge a phone. The wall socket provides $230V$ and the phone needs $5V$. What kind of transformer is inside the charger?

An ideal transformer has $V_p = 240V$, $I_p = 0.5A$, and $V_s = 12V$. What is the secondary current $I_s$?

Which of these would increase the EMF induced in the secondary coil of a transformer?

A step-down transformer has a turns ratio of 10:1. If the secondary voltage is $24V$, what is the primary voltage?

An ideal transformer has $N_p = 100$ and $N_s = 400$. If the power input is $P$, what is the power output?

A transformer with $100\%$ efficiency has $N_p = 500$ and $N_s = 50$. The secondary is connected to a $5.0 \Omega$ resistor. If the primary voltage is $200V$, what is the primary current?

How does the thickness of the copper wire used in the primary and secondary coils of a step-down transformer usually compare?