Tag: ac and dc

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Questions Related to ac and dc

Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

The advantage of ac over dc is that:

  1. its generation cost is much less.

  2. it contains more electric energy.

  3. it is free from voltage fluctuations.

  4. it can be transmitted over long distances with minimum power loss.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Answer is B.

The advantage of AC over DC is that power transmission is simpler under AC, it can be changed in voltage relatively easily using transformers, and that higher power motors can be devised under AC. It contains more electric energy.

Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

Transformer is used for

  1. increasing the voltage.

  2. decreasing the voltage.

  3. both A and B

  4. neither A nor B
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In A.C, voltage can be increased or decreased with the help of a transformer. But in D.C, this cannot be done. Voltage may be increased using a step up transformer and may be decreased using a step down transformer.

Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

State whether the following statement is True or False. 

The induced current produced in a closed coil is always direct current. 

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Answer is B.

AC electricity alternates back-and-forth in direction 50 times per second, according to the electrical system in the country. The charge at the ends of the wire alternates between negative (-) and positive (+). If the charge is negative (-), that pushes the negatively charged electrons away from that terminal. If the charge is positive (+), the electrons are attracted in that direction. Thus the electricity in the wire moves in one direction for a short while and then reverses its direction when the generator armature is in a different position. But if the split ring commutators are attached to the coil then the current will move in the same direction.

Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

Identify the two types of current exist in physics.

  1. direct and alternating

  2. indirect and alternating

  3. direct and attenuating

  4. directive and alternative

  5. none of the answers are correct
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

There exists two types of current -  direct current (dc) and alternating current (ac).

Direct current has constant magnitude and direction whereas the alternating current keeps reversing its direction at regular intervals.

Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

$AC$ and $DC$ can be distinguished using.

  1. heating effect

  2. magnetic effect

  3. chemical effect

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

It is possible to distinguish the AC and DC using magnetic effect. Both AC and DC can produce magnetic field but only AC can produce a varying magnetic field. So, using DC, current cannot be induced into another conductor. It can only be done using AC.

Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

A transistor based radio receiver set (effective resistance of the order of 18 ohms) operates on a 9V dc battery. If this replaced by a dc power supply with rating 9V, 500A then:

  1. Receiver will work normally

  2. Receiver will give distorted output

  3. Receiver will get burnt

  4. Power supply will get over heated
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Answer is A.

In this case, the 9 V battery is replaced with a 9 V power supply. Here, there is no change in the power supply to the radio receiver.
Hence, the receiver will work fine as the voltage supply or power supply remains the same.

Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

Hotwire ammeters are used for measuring _____________ currents.

  1. A.C. only

  2. D.C only

  3. both A.C. and D.C

  4. none of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Hot wire instruments use the Joule’s law of thermal expansion. When a current (AC or DC) is passed through a special wire, the wire heats up due to $(I^2)\times R$ loss. This heating increases the length of the wire. This increase is recorded as the current. The calibrations indicates an aggregate value which goes with both AC and DC measurements. Over usage can tear the wire apart and render it un-usable. These also measure true RMS for an applied AC. 

Hence they are used for measuring both AC and DC.

Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

If $\vartheta $ is the phase difference and T is time period then time difference between current and voltage is ;

  1. $T \vartheta $

  2. $\dfrac { T }{ \vartheta } $

  3. $\dfrac { 2\pi T }{ \vartheta } $

  4. $\dfrac { T \vartheta }{ 2\pi }$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The phase difference theta corresponds to a time difference delta_t. Since 2*pi radians corresponds to one time period T, the ratio is delta_t/T = theta/(2*pi). Thus, delta_t = (T * theta) / (2*pi).