Question

37. Almost all energy sold today is of the AC type because
a. DC voltages don't last.
b. DC energy can’t power televisions.
c. AC voltage is easy to step up and step down.
d. AC energy was established first.

38. Electromagnetic waves travel at a speed
a. equal to the speed of light.
b. greater than the speed of light.
c. less than the speed of light.

39. If 200 W of power goes into the primary coil of a transformer, the power coming from the secondary coil is approximately
a. 2 W.
b. 20 W.
c. 200 W.
d. 2000 W.
e. more than 2000 W.

Answer 1

37. For transfer of electricity, it is useful to transfer it at higher voltages as it results in low power losses. However, electrical appliances will get damaged at this high voltage and hence, it is important to step down the voltage.

So, stepping up and stepping down of voltage is necessary. For this stepping up and stepping down, transformers are used which require AC. So, AC is used because it is easy to step up and step down.

So, option c is correct.

38.All electromagnetic waves travel at speed of light. (option a)

39.In a transformer, power is conserved.

So, power in primary coil=power in secondary coil.

=>power in secondary coil=200 W. (option c)