Tag: thermal effect of electric current

Questions Related to thermal effect of electric current

Heat produced by the resistance R is:

physics effects of electric current joule's law of heating thermal effect of electric current heating effect of electric current

  1. $\displaystyle \frac { VIt }{ 4.2 } $

  2. $\displaystyle \frac { W }{ J } $

  3. $\displaystyle \frac { { i }^{ 2 }Rt }{ 4.2 } $

  4. All

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Correct Option: D
Explanation:

From Joule's Law of heating-


Heat produced$=H=I^2Rt$

Now, $V=IR$

$\implies H=(IR)It=VIt$

And, $I=\dfrac{V}{R}$

$H=I^2Rt=\dfrac{V^2}{R^2}Rt=\dfrac{V^2}{R}t$

In any electric circuit, when the switch is on and the current is flowing through it why do the wire, switches, bulb or devices in the circuit become hot?

physics electric current and its effects thermal effect of electric current heating effect of electric current effect of electric current

  1. Because of the heating effect of electric current

  2. Because of the magnetic effect of electric current

  3. Because of the luminous effect of electric current

  4. None of these

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Correct Option: A
Explanation:

This is because some of the electric energy is converted into heat energy, i.e., heating effect of electric current.

A metal plate can be heated by

physics electric current and its effects thermal effect of electric current heating effect of electric current effect of electric current

  1. passing either a direct or alternating current through the plate.

  2. placing in a time varying magnetic field.

  3. placing in a space varying magnetic field, but does not vary with time.

  4. both (a) and (b) are correct

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Correct Option: D
Explanation:

When a metal plate is getting heated, it may be due to the passage of direct current, alternating current or even induced current through the plate. As time varying magnetic field produces induced current  in the plate, so both (a) and (b) are correct.

When electric current is flown through a conductor, some amount of:

physics electric current and its effects thermal effect of electric current heating effect of electric current effect of electric current

  1. electrical energy is converted into heat energy.

  2. electrical energy is converted into mechanical energy.

  3. mechanical energy is converted into. electrical energy.

  4. heat energy is converted into electrical energy.

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Correct Option: A
Explanation:

A conductor has its own resistance. Due to the flowing current, certain heat is produced in the conductor according to the Joule's heating effect  i.e   $H = I^2Rt$.

Thus electrical energy is converted into heat energy when a current flows through the conductor.

The temperature of a metal wire rises when an electric current is passed through it because:

physics electric current and its effects thermal effect of electric current heating effect of electric current effect of electric current

  1. collision of conduction electrons with the atoms of metal gives them energy which appears as heat

  2. .when electrons fall from higher energy level to lower energy level, heat energy is released

  3. collisions of metal atoms with each other releases heat energy.

  4. collisions of conduction electrons with each other releases heat energy.

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Correct Option: A
Explanation:

Answer is A.

A metallic conductor has a large number of free electrons in it. When a potential difference is applied across the ends of a metallic wire, the free electrons begin to drift from the low potential to the high potential region. These electrons collide with the positive ions (the atoms which have lost their electrons). In these collisions, energy of the electrons is transferred to the positive ions and they begin to vibrate more violently. As a result, heat is produced. Greater the number of electrons flowing per second, greater will be the rate of collisions and hence more heat is produced.
Hence, the temperature of a metal wire rises when an electric current is passed through it because collision of conduction electrons with the atoms of metal gives them energy which appears as heat.

When a current flows through a conductor, its temperature

physics electric current and its effects thermal effect of electric current heating effect of electric current effect of electric current

  1. increases

  2. decreases

  3. remains same

  4. may increase or decrease

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Correct Option: A
Explanation:

As we know,

$Power=I^2R$
Therefore, this power is released in the form of heat in the conductor and this heat increases the temperature of the conductor.
Hence, temperature increases.

A lamp is marked 60 W, 220 V. If it operates at 200 V, the rate of consumption of energy will _____

physics electric current and its effects thermal effect of electric current heating effect of electric current effect of electric current

  1. decrease

  2. increase

  3. remain unchanged

  4. first increase then decrease

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Correct Option: A
Explanation:
Given power of bulb =60W
Voltage=220V
Power $=\dfrac{V^2}{R}$
$60=\dfrac{220\times220}{R}$
$R=(\dfrac{220\times220}{60})\Omega$
$R=(\dfrac{220\times22}{6})\Omega$         (1)
When voltage = 200V, resistance will be same
$P=\dfrac{200\times200}{R}$
From 1,
$=\dfrac { 200\times 200\times 6 }{ 220\times 22 } $
$\dfrac { 200\times 20\times 6 }{ 22\times 22 } $
$=49.5J/S$

We see that  power gets decrease.
Power = rate of consumption of energy,
So rate of consumption of energy.

The amount of heat produced in a wire depends on its material-

physics electric current and its effects thermal effect of electric current heating effect of electric current effect of electric current

  1. Length

  2. Thickness

  3. Length and thickness

  4. None of these

Show answer
Correct Option: C
Explanation:

Amount of heat produced in wire = $I^2R$

Where $R$ = Resistance of wire
            $I$ = Current through wire
As resistance of wire   $R \propto   \dfrac{L}{A}$
So heat produced depends on Length as well as thickness.        

Heat produced in a resistor when current is passed through it depends upon-

physics electric current and its effects thermal effect of electric current heating effect of electric current effect of electric current

  1. Current only

  2. Time only

  3. Current and time

  4. None of these

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Correct Option: C
Explanation:

$Power=i^2R$

and $Energy=Heat=Power\times time=I^2Rt$

One megawatt is equivalent to

physics electric current and its effects thermal effect of electric current heating effect of electric current effect of electric current

  1. $\displaystyle 10^{2}W$

  2. $\displaystyle 10^{6}W$

  3. $\displaystyle 10^{4}W$

  4. $\displaystyle 10^{8}W$

Show answer
Correct Option: B
Explanation:

Prefix Mega means $ 10^6 $.

So, 1 Megawatt = $10^6$ W