A circuit has a resistance of 12 Ω and an impedance of 15 Ω. The power factor of the circuit will be

• 0.8

• 0.4

• 1.25

• 0.125

The teachers of Geeta’s school took the students on a study trip to a power generating station, located nearly 200 km away from the city. The teacher explained that electrical energy is transmitted over such a long distance to their city, in the form of alternating current (ac) raised to a high voltage. At the receiving end in the city, the voltage is reduced to operate the devices. As a result, the power loss is reduced. Geeta listened to the teacher and asked questions about how the ac is converted to a higher or lower voltage.

1. Name the device used to change the alternating voltage to a higher or lower value. State one cause for
   power dissipation in this device.
2. Explain with an example, how power loss is reduced if the energy is transmitted over long distances as an alternating current rather than a direct current.
3. Write two values each shown by the teachers and Geeta.

A current I flows along the length of an infinitely long, straight, thin walled pipe. Then 

The phase difference between the alternating current and emf is π/2. Which of the following cannot be the constituent of the circuit?

Alternating current can not be measured by D.C. ammeter because

In an LCR series a.c. circuit, the voltage across each of the components, L, C and R is 50 V. The voltage across the LC combination will be