## March 6, 2015

### 10th Class Physical Sciences Important 2 Marks Questions

Q: How do you appreciate Faraday's Laws, which is the consequence of conservation of energy. (2 marks)
A: 'Energy can neither be created one destroyed. But it can be converted from the form to other'. - This is law of conservation of energy. 'When there is a change of magnetic flux linked with a closed coil, a current is generated in the coil. This induced E.M.F. is equal to the rate of change of magnetic flux passing through 'it'. - This is Faraday's Law.

To move the magnet in the coil, some work is to be done. This work produces energy which is converted into electrical energy in the coil.
This is how conservation of energy takes place in electromagnetic induction.

Q: State Kirchhoff's Laws. (2 marks)
A: Kirchhoff's Junction Law: At any junction point in a circuit when the current can divide, the sum of the currents into the junction must equal to the sum of the currents leaving the junction.

The Loop Law: The algebraic sum of the increases and decreases in potential difference across various components of a closed circuit loop must be zero.

Q: How could we use the principle of electromagnetic induction in the case of using ATM Card when its magnetic strip is swiped through a scanner.
(2 marks)

A: If the card is moved through a card reader, then a change in magnetic flux is produced in one direction, which induces e.m.f. or potential. The current received by the pickup coil goes through signal amplification and translated into binary code, so that it is read by the computer.

Q: A house has 3 tube lights, two fans and a television. Each tube light draws 40 W. The fan draws 80 W and television draws 60 W. On the average all the tube lights are kept on for five hours, two fans for 12 hours and the television for five hours every day. Find the cost of electric energy used in 30 days at the rate of Rs.3.00 per KWh. (4 marks)

A: Power consumed by 3 tube lights in a day = 40 W × 3 × 5 h = 600 Wh
Power consumed by 2 fans in a day = 80 W × 2 × 12 h = 1920 Wh
Power consumed by 1 television in a day = 60 W × 1 × 5 h = 300 Wh
Total power consumed in the house per day = 600 Wh + 1920 Wh + 300Wh = 2820 Wh
Total power consumed in the house per month(30 days) = 2820 Wh × 30 = 84,600 Wh 84,600
Total power consumed in K.Wh = 84600 / 1000 = 84.6 KWh
Rate per KWh = Rs.3
Cost of 84.6 KWh electrical energy consumed = Rs.84.6 × 3 = Rs.253.80.