Tag: ac vs dc

Questions Related to ac vs dc

The advantage of ac over dc is that:

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

  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.

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Correct Option: B
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.

Transformer is used for

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

  1. increasing the voltage.

  2. decreasing the voltage.

  3. both A and B

  4. neither A nor B

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Correct Option: C
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.

State whether the following statement is True or False. 

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

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

  1. True

  2. False

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Correct Option: B
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.

Identify the two types of current exist in physics.

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

  1. direct and alternating

  2. indirect and alternating

  3. direct and attenuating

  4. directive and alternative

  5. none of the answers are correct

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Correct Option: A
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.

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

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

  1. heating effect

  2. magnetic effect

  3. chemical effect

  4. none of these

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Correct Option: B
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.

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:

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

  1. Receiver will work normally

  2. Receiver will give distorted output

  3. Receiver will get burnt

  4. Power supply will get over heated

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Correct Option: A
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.

An A.C. source is rated $220V,50Hz$. The average voltage is calculated in a time interval of $0.01s$, it-

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

  1. must be zero

  2. may be zero

  3. is never zero

  4. is $\frac { 20 }{ \sqrt { 2 } } $ volt.

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Correct Option: A

Hotwire ammeters are used for measuring _____________ currents.

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

  1. A.C. only

  2. D.C only

  3. both A.C. and D.C

  4. none of these

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Correct Option: C
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.

As the frequency of an alternating current increases, the impedance of the circuit

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

  1. increases continuously

  2. decreases continuously

  3. remains constant

  4. None of these

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Correct Option: B

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

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

  1. $T \vartheta $

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

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

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

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Correct Option: D