Question 1: Define a magnetic field and describe how magnetic field lines are used to represent it.

Answer: A magnetic field is a region around a magnetic material within which the force of magnetism acts. Magnetic field lines are used to visualise the direction and strength; they emerge from the north pole and enter the south pole, with the density indicating the field's strength.

Question 2: Explain why a compass needle aligns along magnetic field lines.

Answer: Because the needle is a small magnet, it experiences a torque that aligns it along the magnetic field lines where the magnetic force is strongest.

Question 3: State the units used for magnetic flux density.

Answer: Tesla (T)

Question 4: Describe how the magnetic field strength varies with distance from a bar magnet.

Answer: The magnetic field strength decreases as the distance from the magnet increases, following approximately an inverse square law in the space around the magnet.

Question 1: A straight conductor carrying a current of 5 A is placed in a magnetic field with a flux density of 0.2 T. If the length of the conductor within the magnetic field is 0.5 m and the angle between the conductor and the magnetic field is 90°, calculate the magnetic force on the conductor. (Use F = BIL sin θ)

Answer: F = 0.5 N

Question 2: Calculate the magnetic flux density if a magnetic field exerts a force of 2 N on a wire of length 1 m carrying a current of 3 A at an angle of 60° to the field. (Use F = BIL sin θ)

Answer: B ≈ 4.62 T

Question 1: Describe a simple experiment to demonstrate the presence of a magnetic field around a current-carrying wire. Include the variables involved and safety precautions.

Answer: A suitable experiment involves passing a current through a straight wire and placing iron filings around it to visualise the magnetic field pattern. Variables include current (independent), number of filings (dependent), and wire position (controlled). Safety precautions include ensuring the wire is securely mounted, avoiding contact with live wires, and using appropriate current levels to prevent overheating.

Question 2: Explain why electromagnetic devices such as electric motors rely on magnetic fields.

Answer: Electric motors rely on magnetic fields to produce a force on current-carrying conductors, which creates torque to produce rotational movement, converting electrical energy into mechanical energy.

Question 1: A coil of wire with 50 turns is placed in a magnetic field with a flux density of 0.3 T. The coil experiences a change in magnetic flux of 0.015 Weber over 0.5 seconds. Calculate the induced emf in the coil.

Answer: E = 1.5 V

Question 2: Interpret the data: What does the change in magnetic flux imply about the magnetic field or the coil's movement?

Answer: It indicates that either the magnetic flux through the coil has changed, perhaps due to movement within a magnetic field or a change in the field's strength, inducing an emf according to Faraday's law.

Question 1: Describe how magnetic resonance imaging (MRI) uses magnetic fields to produce images of the human body.

Answer: MRI uses strong, uniform magnetic fields and radio waves to excite hydrogen nuclei in the body. When these nuclei relax, they emit signals that are detected and processed to produce detailed images of tissues and organs.

Question 2: Explain the role of magnetic fields in electric generators used in power stations.

Answer: Magnetic fields in electric generators induce an emf in coils of wire as they rotate within the magnetic field, converting mechanical energy into electrical energy based on electromagnetic induction.