7. A toaster has a power rating of 1050 W when it is connected to the mains supply.
Its heating coil is made of nichrome and it has a resistance of 12 Ω. The coil is 40 m long and it has a circular cross-section of diameter 2.2 mm. Calculate: (i) the resistivity of nichrome
(ii) the heat generated by the toaster in 2 minutes if it has an efficiency of 96%.
(18)
8. A bar magnet is attached to a string and allowed to swing as shown in the diagram. A copper sheet is then placed underneath the magnet.
Explain why the amplitude of the swings decreases rapidly.
What is the main energy conversion that takes place as the magnet slows down?
(12) (6)
A metal loop of wire in the shape of a square of side 5 cm enters a magnetic field of flux density 8 T.
The loop is perpendicular to the field and is travelling at a speed of 5 m s–1. (i) How long does it take the loop to completely enter the field?
(ii) What is the magnetic flux cutting the loop when it is completely in the magnetic field?
(iii) What is the average emf induced in the loop as it enters the magnetic field?
(20) 2007
8. The dome of a Van de Graaff generator is charged. The dome has a diameter of 30 cm and its charge is 4 C. A 5 μC point charge is placed 7 cm from the surface of the dome.
Calculate: (i) the electric field strength at a point 7 cm from the dome (ii) the electrostatic force exerted on the 5 μC point charge.
2005
9. Two resistors, of resistance R1 and R2 respectively, are connected in parallel. Derive an expression for the effective resistance of the two resistors in terms of R1 and R2.
At room temperature, calculate (i) the total resistance of the circuit (ii) the current flowing through the 750 Ω resistor.
6 V (12)
In the circuit diagram, the resistance of the thermistor at room temperature is 500 Ω.
