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

A metal plate can be heated by

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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

  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.
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  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.
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

When a current flows through a conductor, its temperature

  1. increases

  2. decreases

  3. remains same

  4. may increase or decrease
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  1. decrease

  2. increase

  3. remain unchanged

  4. first increase then decrease
Reveal answer Fill a bubble to check yourself
A Correct answer
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.
Multiple choice physics electric current and its effects thermal effect of electric current heating effect of electric current effect of electric current

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

  1. Length

  2. Thickness

  3. Length and thickness

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