Board Previous Year Questions (PYQs)
Arranged by marks. State rules precisely and draw labelled diagrams where asked (they carry marks).
1-Mark Questions
Q1. Name the rule that gives the direction of the magnetic field around a straight current-carrying conductor. (Ans: right-hand thumb rule.)
Q2. What is the frequency of AC supply in India? (Ans: 50 Hz.)
Q3. Name the colour of insulation of the earth wire. (Ans: green.)
Q4. Which rule gives the direction of the induced current? (Ans: Fleming's right-hand rule.)
Q5. What kind of magnet is a current-carrying solenoid with a soft-iron core called? (Ans: an electromagnet.)
2-Mark Questions
Q6. State the properties of magnetic field lines (any two). Ans: (i) They run from the north pole to the south pole outside the magnet and form closed loops. (ii) They never cross each other. (iii) They are crowded where the field is stronger.
Q7. Distinguish between an AC generator and a DC generator. Ans: An AC generator uses two slip rings, giving an output current that reverses each half turn (alternating current). A DC generator uses a split-ring commutator, giving current in one direction (direct current).
Q8. Why is the fuse connected in the live wire and not the neutral wire? Ans: So that when the fuse melts, it disconnects the appliance from the live (high-potential) wire, making the appliance safe to touch. A fuse in the neutral wire would leave the appliance connected to the live wire even after blowing.
3-Mark Questions
Q9. State Fleming's left-hand rule and name two devices based on it. Ans: Stretch the thumb, forefinger and middle finger of the left hand mutually perpendicular; if the forefinger points along the field and the middle finger along the current, the thumb gives the force (motion). Devices: electric motor, loudspeaker (also microphones, measuring instruments).
Q10. A 2 kW electric oven is connected to a 220 V, 5 A circuit. Explain what happens. Ans: Current A, which exceeds the 5 A rating. The fuse blows and breaks the circuit, so the oven cannot operate on this circuit.
Q11. What is an electromagnet? Why is soft iron used for its core? Ans: An electromagnet is a soft-iron core wrapped with a coil of insulated wire that becomes magnetic when current flows. Soft iron is used because it magnetises strongly with current and loses its magnetism when the current stops, allowing the magnet to be switched on and off.
5-Mark Questions
Q12. (a) Draw a labelled diagram of an electric motor. (b) State its principle. (c) What is the function of the split-ring commutator? Ans: (a) Diagram: coil ABCD between magnet poles N–S, split-ring commutator, carbon brushes, battery. (b) Principle: a current-carrying coil in a magnetic field experiences a force (torque) - Fleming's left-hand rule - that rotates it; it converts electrical to mechanical energy. (c) The split-ring commutator reverses the current in the coil every half rotation, keeping the torque in the same sense so the coil rotates continuously.
Q13. (a) What is electromagnetic induction? (b) State Fleming's right-hand rule. (c) Name and give the energy conversion of the device based on it. Ans: (a) The production of an induced current in a conductor when the magnetic field through it changes (Faraday). (b) With the right hand's thumb, forefinger and middle finger mutually perpendicular: forefinger = field, thumb = motion, middle finger = induced current. (c) The electric generator, which converts mechanical energy into electrical energy.
Q14. Describe the domestic electric circuit: name the three wires with their colours, state the supply voltage and frequency, and explain earthing. Ans: Three wires: live (red), neutral (black), earth (green). Supply: AC, 220 V, 50 Hz. Appliances are in parallel, each with a switch and fuse on the live wire. Earthing connects the metal body of appliances to a buried earth plate via the green wire, giving leakage current a low-resistance path to ground and protecting the user from severe electric shock.