Tag: physics

Questions Related to physics

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

The resistance of a coil for dc is $R$ ohms. When connected to ac supply the total resistance offered by circuit to ac current.

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

  1. Will remain same

  2. Will increase

  3. Will decrease

  4. Will be zero

Show answer
Correct Option: A
Explanation:

Resistance offered by coil is same for $AC$ as well as $DC.$ So, Resistance will not change.

Consider the following statements:
(a) The magnitude and direction of alternating current reverses periodically.
(b) Frequency of alternating current in india is 50 Hz.
(c) The frequency of direct current is zero.
Which of the above statements are correct?

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

  1. (b) and (c)

  2. (a) and (b)

  3. All of them

  4. None of them

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Correct Option: C
Explanation:

Electricity flows in two ways: either in an alternating current (AC) or in a direct current (DC).
Electricity or "current" is nothing but the movement of electrons through a conductor, like a wire. The difference between AC and DC lies in the direction in which the electrons flow. In DC, the electrons flow steadily in a single direction, or "forward." In AC, electrons keep switching directions, sometimes going "forward" and then going "backward." Alternating current is the best way to transmit electricity over large distances. 

Choose the correct option

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

  1. In Direct Current, Magnitude and direction of current is constant

  2. In Direct Current, Magnitude and direction of current reverses periodically

  3. In Alternating Current, Magnitude and direction of current is constant

  4. Direct current is periodic in nature

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Correct Option: A
Explanation:

Direct current is categorized by current of constant magnitude and direction.