Tag: heating effect of electric current

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

An air conditioner is rated $240\ V, 1.5\ kW$. The air conditioner is switched on $8\ hrs$ each day. What is electrical energy consumed in $30\ days$?

  1. $2.88\ kWh$
  2. $360\ kWh$
  3. $120\ kWh$
  4. $240\ kWh$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Energy consumed is given by:

$E= Pt$
    $= 1.5 KW \times  30 \times 8 hrs= 360 KWh $

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

Two electric bulbs rated ${P} _{1}$ and  watt at $V$ volt are connected in series across $V$ volt mains, then their total power consumption $P$ is

  1. $\left( { P } _{ 1 }+{ P } _{ 2 } \right) $
  2. $\sqrt { { P } _{ 1 }{ P } _{ 2 } } $
  3. $\dfrac {P _{1}+P _{2}}{2} $
  4. $\dfrac {P _{1}P _{2}}{P _{1}+P _{2}} $
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Resistance of Ist bulb $={ R } _{ 1 }=\cfrac { { V }^{ 2 } }{ { P } _{ 1 } } $
Resistance of IInd bulb $={ R } _{ 2 }=\cfrac { { V }^{ 2 } }{ { P } _{ 2 } } $
when both bulbs are connected in series
$\quad { R } _{ eq }={ V }^{ 2 }\left[ \cfrac { 1 }{ { P } _{ 1 } } +\cfrac { 1 }{ { P } _{ 2 } }  \right] =\cfrac { { V }^{ 2 }\left( { P } _{ 1 }+{ P } _{ 2 } \right)  }{ { P } _{ 1 }{ P } _{ 2 } } $
Hence, power consumed $P=\cfrac { { V }^{ 2 } }{ R } =\cfrac { { V }^{ 2 } }{ { V }^{ 2 }\left( \cfrac { { P } _{ 1 }+{ P } _{ 2 } }{ { P } _{ 1 }{ P } _{ 2 } }  \right)  } =\cfrac { { P } _{ 1 }{ P } _{ 2 } }{ { P } _{ 1 }+{ P } _{ 2 } } \quad $

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

An electric bulb is connected to a $20$ V battery of negligible internal resistance. The resistance offered by the bulb is $5$ $\Omega$. The electrical energy consumed by the bulb in $3$ hours is _____ kWh.

  1. $0.12$
  2. $0.24$
  3. $0.06$
  4. $0.03$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Power consumed by bulb is $P=\dfrac{V^2}{R}$


Energy$=E=Pt=\dfrac{V^2}{R}t=\dfrac{20^2}{5}W\times 3h$

$\implies E=240Wh=0.24kWh$

Answer-(B)

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

What should be the bill for the month of April for a heater of resistance 60.5 $\Omega$ connected 220 V mains, The cost of energy is Rs 2 per kWh and the heater is used for 3 hours daily?

  1. $Rs\ 144$
  2. $Rs\ 222$
  3. $Rs\ 662$
  4. $Rs\ 238$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Power of heater $=P=\dfrac{V^2}{R}$


Energy used in one month$=E=Pt=\dfrac{V^2}{R}\times 3\times 30$

$\implies E=\dfrac{220\times 220}{60.5}\times 90Wh=\dfrac{484\times 9}{60.5}kWh=72kWh$

Hence cost$=72\times 2=Rs144$

Answer-(A)

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

Laws of heating is given by :

  1. Joule

  2. Ohm

  3. Maxwell

  4. Faraday
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Answer is A.

The heat which is produced due to the flow of  current   within an electric wire, is expressed in Joules.
James Prescott Joule was an English physicist who studied the nature of heat and established its relationship to mechanical work. He therefore laid the foundation for the theory of conservation of energy, which later influenced the First Law of Thermodynamics. He also formulated the Joules laws which deal with the transfer of energy.

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

An electric fan is switched on in a closed room. The air in the room is 

  1. cooled

  2. heated

  3. maintains its temperature

  4. heated or cooled depending on the atmosphere
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If an electric fan is switched on in a closed room, the air will be heated because due to motion of the fan, the speed of air molecules will increase. In fact, we feel cold due to evaporation of our sweat