Electricity and Magnetism

St. Xavier's School

H.Hw. Physics: Electricity and Magnetism

1. You take two resistors of resistance 2R and 3R and connect them in parallel in an electric circuit. Calculate the ratio of the electrical power consumed by 2R and 3R?
2. Calculate the resistance of 2 km long copper wire of radius 2 mm. (Resistivity of copper = 1.72 x 1 0-8)
3. A 250 watt electric bulb is lighted for 5 hours daily and four 6 watt bulbs are lighted for 4.5 hours daily. Calculate the energy consumed (in kWh) in the month of February.
4. State and derive joule’s law. An electric iron consumes energy at rate of 420w when heating is at maximum rate and 180 w when heating is at minimum. The voltage is 220V .What is the current and resistant in each case?
5. A small bulb has a resistance of 2Ω when cold. It takes up a current of 0.4 A from a source of 4V and then starts glowing. Calculate (i) the resistance of the bulb when it is glowing.(ii)  Elaborate on the reason for the difference in resistance?
6. Draw magnetic field lines due to:   a) Straight conductor (b) Solenoid (c) Circular wire
7. Explain kicking wire experiment and draw conclusion from it.
8. Differentiate between temporary magnet and permanent magnet.  Which of them is commercially more useful?