Electricity-Sample Questions

1.  Name the unit of (a) electrical resistance (b) resistivity

2.  Define One Ohm

3.  Define Resistivity

4.  Determine the direction of conventional current?

5.  What is electrical power? Write its unit.

6.  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?

7.  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 and

      (ii)  Elaborate on the reason for the difference in resistance?

8.  Define resistance and resistivity and also give the relation between them. Explain the dependence of resistance on temperature.

9.  A bulb is rated at 330V- 110W. What do you think is its resistance? Three such bulbs burn for 5hrs at a stretch. What is the energy consumed? Calculate the cost in rupees if the rate is 70 paise per unit?

10.  Calculate the resistance of 2 km long copper wire of radius 2 mm. (Resistivity of copper = 1.72 x 1 0^-8)

11.  What connection is used in domestic appliances and why?

12.  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.

13.  A torch bulb is rated at 3V and 600mA. Calculate it’s

        (a)  Power b) Resistance c) Energy consumed if it is lighted for 4 Hrs.

14.  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?

15.  A piece of wire having a resistance R is cut into five equal parts.

        (i)  How will the resistance of each part of the wire compare with the original resistance?

        (ii)  If the five parts of the wire are placed in parallel, how will the resistance of the combination compare with the resistance of the original wire? What will be ratio of resistance in series to that of parallel?