Direct Current vs. Alternating Current

Q.

Why is AC preferred over DC?

Q.

Which of the following does not show the property of an alternating current?

1. It reverses its direction periodically.

2. Its frequency is 50Hz for households in India.

3. AC can be transmitted over longer distances than DC.

4. Its magnitude is constant.

Q. A current carrying wire gets heated up due to:

1. its weight.
2. its resistance to current flow.
3. its colour.
4. direction of current through it.

Q.

Which of the following is used in automobile radiators?.

1. Iron

2. Steel

3. Copper

4. Aluminium

Q.

Why do we use alternating current?

Q.

At a neutral point, the resultant magnetic field is :

1. zero

2. along E - W

3. maximum

4. along N - S

Q. Which of the following are advantages of AC over DC ?

1. Easily stepped up and down for long transmission with fairly low loss
2. Easy to generate with AC Generator/motor from rotary sources (e.g. turbines)
3. Easy to make powerful, reliable motors (induction type)
4. all of the above

Q.

What is electrical current that reverses its direction at a regular interval called?

1. Alternating Current

2. Direct Current

3. Electron current

4. Conventional Current

Q.

What is a D.C? Name a device producing DC.

Q. At what voltage is the electric power from generating station transmitted ?

1. $200kV$
2. $11kV$
3. $220kV$
4. $220V$

Q.

Name two small sources of electric current and four devices in which they are used.

Q. Mention the advantage of alternating current over direct current.

Q.

Explain why Ac is preferred over DC for transmission over long distance

Q. High voltage transmission results in lower current and hence lower heat loss. AC is preferred over DC because

1. Voltage level transformation is easier in AC at same power levels.
2. Voltage level transformation is easier in DC at same power levels.
3. AC Voltage levels are always greater than DC Voltage levels.
4. None of the above

Q. In alternating current, the direction of current flow through a circuit changes continuously.

1. True
2. False

Q. State one advantage of using a.c. over d.c.

Q. Electric power is transmitted over long distance through conducting wires of very high voltage, because.

1. The power losses are reduced to minimum
2. Signals of high voltages travel faster
3. Of economical reasons
4. High voltages can be stepped down to desired levels easily

Q. The Joules heating effect for an electric heater in A.C and in D.C. circuit is

1. Equal
2. nearly Equal
3. not equal
4. opposite

Q. Voltage and current in an ac circuit are given by $V=5sin(100\pi -\frac{\pi }{6})$ and $I=4sin(100\pi +\frac{\pi }{6})$

1. Voltage leads the current by ${30}^0$
2. Current leads the voltage by ${30}^0$
3. Current leads the voltage by ${60}^0$
4. Voltage leads the current by ${60}^0$

Q. In alternating current, the direction of current flow through a circuit changes continuously.

1. True
2. False

Q. Which of the following are the sources of direct current?

1. DC generator
2. Batteries
3. Solar cells
4. None of these.

Q. Why are transmission losses so crucial that electrical power systems are designed to work on Alternating currents?

1. Electrical power systems are not very efficient for transmission of power
2. It is a practice to use AC over DC
3. AC networks are easier to handle than DC Networks and constructional setup cost is really high in DC
4. Since, power stations are very far away from destinations, transmission has to be done over long distances and losses add up over the distance

Q. Answer the following questions:
(i) What is the direction of magnetic field lines outside a bar-magnet?
(ii) The magnetic field lines in a given region are getting crowded. What does it indicate?
(iii) State one advantage of AC over DC.

Q. Distinguish between d.c. and a.c.?

Q. The electricity that we use at home to run appliances is __________ current.

1. transforming
2. operating
3. direct
4. alternating

Q. On which principle A.C generator works?

Q. If the r.m.s. value of A.C. is $l_{rms}$ then peak value is -

1. $\sqrt{2}{l}_{rms}$
2. $l_{rms}/\sqrt{2}$
3. $2\sqrt{2}{l}_{rms}$
4. $2l_{rms}$

Q. So that your grandmother can listen to A Prairie Home Companion, you take her bedside radio to the hospital where she is staying. You are required to have a maintenance worker test the radio for electrical safety. Finding that it develops $120V$ on one of its knobs, he does not let you take it to your grandmother’s room. Your grandmother complains that she has had the radio for many years and nobody has ever gotten a shock from it. You end up having to buy a new plastic radio.
(a) Why is your grandmother’s old radio dangerous in a hospital room?
(b) Will the old radio be safe back in her bedroom?

Q. Why do we prefer AC for transmission to long distances while most of the appliances are based on DC ?

Q. Generation of Alternating Current in India is done at

1. 45 Hz
2. 50 Hz
3. 60 Hz
4. 55 Hz