Tag: effect of electric current

Quizzes (11) Questions (54)

Questions Related to effect of electric current

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

Which of the following will produce maximum wastage of electricity ?

  1. CFL

  2. Electric bulb

  3. LED lights

  4. All are power savers
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Electric bulb works by heating up a small wire called a filament. Electric current heats the filament so much that it glow. In fact, $90\%$ of the electricity used by a electric bulb is converted to heat and this conversion will produce maximum wastage of electricity.

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

Several electric bulbs designed to be used on a 220 V electric supply are rated 20 W each. How many lamps can be connected in parallel with each other across the two wires of 220 V line, if the maximum allowable current is 5 A?

  1. 50

  2. 110

  3. 55

  4. 60
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Total power P = V * I = 220 V * 5 A = 1100 W. Since each bulb is 20 W, the number of bulbs n = 1100 / 20 = 55.

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

An electric heater kept in vacuum is heated continuously by passing electric current. Its temperature:

  1. will go on rising with time

  2. will stop after sometime as it will loose heat to the surroundings by conduction

  3. will rise for sometime and thereafter will starts falling

  4. will become constant after sometime because of loss of heat due to radiation
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Treating initially that there is no radiation and on applying voltage to the heater, the temperature of the heater rises. As the temperature rises, the radiation also increases.
As the input power($i^2r$) is constant, the output power should also be constant.
Initially temperature will be increasing and  radiation as well. When the heater reaches a certain temperature, the radiation power equals the input power and the temperature of the heater stops rising.
Thus temperature becomes constant after some time.  

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

Choose the incorrect option: Expansion during heating:

  1. occurs only in a solid

  2. increases the density of the material

  3. decreases the density of the material

  4. occurs at the same rate for all liquids and gaseous.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
$A)$ The incorrect sentence is option $A$ because expansion during heating occurs in all kinds of substance. Solid, liquid, and gas expanse when heated. The reason is this, all materials, as you know, are made up of atoms. The kinetic enery of the materials and their atoms move or vibrate more at any temperature above absolute $0$ ($-273$ degree celsius). Thus the atoms take up more space upon heating and the material expands.
The other options are true.
$B)$ A hot material is heavier than the cold one. So it is true.
$C)$ During heating, the molecules expand and they create more distance between them. Thus heating decreases the density of the material.
$D)$ This option is also quite wrong because not all solids and liquids (or gas, per say) expand at the same rate. The reason is this, at same temperature, solid expands the lesser than liquid, and gasses the most.
Multiple choice physics electric current and its effects thermal effect of electric current heating effect of electric current effect of electric current

A coil and a bulb are connected in series with a $12$ volt direct current source. A soft iron core is now inserted in the coil. Then

  1. The intensity of the bulb remains the same

  2. The intensity of the bulb decreases

  3. The intensity of the bulb increases

  4. Nothing can be said
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In a DC circuit, the soft iron core increases the inductance of the coil. However, since the current is steady DC, the inductive reactance is zero, so the intensity of the bulb remains unchanged.

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

Appliances based on heating effect of current work on

  1. only A.C.

  2. only D.C.

  3. both A.C. and D.C.

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

As  heat produced depends upon resistance which has no relation with AC or DC but heat produced  also depends upon current as $H \propto\  I^2$ so for heating effect both A.C. and D.C. can be used, that's why appliances based on heating effect can work on AC as well as DC. hence correct option is C.

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

Fill in the blank.

The heat generated in calorie is equal to _________.

  1. $ VIt$
  2. $(VIt)/4.2 $
  3. $(V^2Rt)/4.2 $
  4. $VI^2t$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The right matches are given below.
Heat Generated$\rightarrow $Propotional to the square of current$\rightarrow $ $\frac { VIt }{ 4.18 } cal$  
Resistance in parallel$\rightarrow $Is used to reduce effective resistance in a circuit$\rightarrow $  $\frac { 1 }{ { R } _{ p } } =\frac { 1 }{ { R } _{ 1 } } +\frac { 1 }{ { R } _{ 2 } } $
Resistivity$\rightarrow $Depends on the material of the conductor$\rightarrow $  $\rho =\frac { RA }{ l } $
Ohm's law$\rightarrow $Gives relation between V and I$\rightarrow $V=IR

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

A copper voltameter is connected in series with a coil of resistance $10 \Omega $. When a steady current is passed through the circuit, $0.297 g$ of copper is found to be deposited at the cathode in $15 min$. The electrochemical equivalent of copper is $3.3 \times 10^{-7} kg C^{-}$. Heat liberated in the coil is:

  1. $900 J$
  2. $90 J$
  3. $9 J$
  4. $9 kJ$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$\displaystyle I = \frac {m}{Zt} = \frac {297 \times 10^{-6}}{3.3 \times 10^7 \times 15 \times 60}=1A$

$H = I^2Rt = 1 \times 10 \times 15 \times 60$
$=9000J = 9kJ$

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

Rate of dissipation of Joules heat in resistance per unit volume is (symbols have usual meaning)

  1. $\sigma E$
  2. $\sigma J$

  3. J E

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

The differential form of the Joule heating equation gives the power per unit volume.

$\cfrac {dp}{dv}=J.E$
Here, $J=$ Current Density
          $E=$ Electric Field.