Tag: physics

Questions Related to physics

A bulb  is connected  to an ideal battery of emf 10 V so that the resulting current is 10 mA . When the bulb is connected to 220 V mains (ideal), the current is 50 mA. choose the correct alternative

physics alternating currents sinusoidal current types of current movement of charge

  1.   the resistance of the bulb is 1 k ohm and in the second case, it is 4.4 k ohm

  2. it is not possible since ohm's law is not followed

  3.  the increase in resistance is due to heating of the filament of the bulb when it is connected to 220 V main

  4. none of these

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Correct Option: A
Explanation:

A bulb is connected to an ideal battery of emf$=10V$

Current$=10mA\=10\times10^{-3}A$
when the bulb connected $220V$ (main)
and current$=50\times10^{-3}A$
Using Ohm's law,
First case:
$I=\cfrac{10\times10^3}{10}=1K\Omega$
Second case 
$I^{\prime}=\cfrac{220\times10^3}{50}=4.4k\Omega$
Hence answer $(A)$ will be correct.

In a transformer the immediate cause of the induced A. C. in the secondary coil is

physics alternating currents sinusoidal current types of current movement of charge

  1. A varying electric field

  2. A varying magnetic field

  3. A motion of the secondary coil

  4. Efficiency of the operator

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Correct Option: B

Alternating current is one which changes in its :

physics alternating currents sinusoidal current types of current movement of charge

  1. direction

  2. magnitude

  3. magnitude and direction both

  4. none

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Correct Option: C
Explanation:

Answer is C.

An alternating current (AC) is an electric current of which magnitude and direction vary, unlike direct current, whose direction remains constant.
The usual waveform of an AC power circuit is a sine wave, because this leads to the most efficient transmission of energy. However, in certain applications different waveforms are used, such as triangular or square waves.

An alternating voltage is given by $e = (6\sin \omega t + 8\cos \omega t)volt$. The instantaneous value of voltage is given by

physics alternating currents sinusoidal current types of current movement of charge

  1. $5\sqrt {2}V$

  2. $10V$

  3. $10\sqrt {2}V$

  4. $\dfrac {10}{\sqrt {2}}V$

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Correct Option: B

State whether given statement is True or False
The designation rms means repetitions measured per second.

physics alternating currents sinusoidal current types of current movement of charge

  1. True

  2. False

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Correct Option: B
Explanation:

The dsignation rms means Root Mean Square Value of a quantity such as RMS value of current, voltage in an ac circuit.

The simplest type of AC voltage or current is the one which

physics alternating currents sinusoidal current types of current movement of charge

  1. Varies exponentially

  2. Varies sinusoidally

  3. Varies linearly

  4. Does not vary uniformly

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Correct Option: B
Explanation:

Solution:-

AC wave can be of any form but mathematical techniques are easier for the sine waveform such as any wave can be represent as combination of sine waves using fourier transform and integration and differentiation of sine wave is sine wave only.

Option B is correct.

Choose the incorrect statement.

physics alternating currents sinusoidal current types of current movement of charge

  1. Alternating current is oscillatory

  2. Electric power is transmitted over long distances using alternating current.

  3. Frequency of alternating current in India is 50 Hz.

  4. Alternating current can be used for electrolysis of copper chloride.

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Correct Option: D
Explanation:

Even if it were current-limited, alternating current (AC) would not be appropriate for electrolysis. Because the "cathode" and "anode" will be constantly switching places as the polarities will change with time. Therefore, direct current (DC) is used for electrolysis.

Why the current produced by the generator is  called as alternating current.

physics alternating currents sinusoidal current types of current movement of charge

  1. continuous decrease and increase of current occurs.

  2. after every half cycle direction of flow of current is reversed.

  3. both

  4. none

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Correct Option: B
Explanation:

We may say that after every half cycle direction of flow of current is reversed. Because of this reason the current produced by the generator is also called as alternating current.

A coil, a capacitor and an ac source of rms voltage $24V$ are connected in series. By varying the frequency of the source, a maximum rms current of $6A$ is observed. If this coil is connected to a battery of emf $12V$ and internal resistance $4\Omega$, the current through will be

physics alternating currents sinusoidal current types of current movement of charge

  1. $2.4A$

  2. $1.8A$

  3. $1.5A$

  4. $1.2A$

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Correct Option: C

A mixer of $1000\Omega$ resistance is connected to an $A.C.$ source of $200\ volts$ and $50\ cycle/sec$. The value of average potential difference across the mixer will be:

physics alternating currents sinusoidal current types of current movement of charge

  1. $308\ volts$

  2. $264\ volts$

  3. $220\ volts$

  4. $zero$

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Correct Option: D