Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

Multiple choice physics transfer of heat applications of convection convection thermal energy transfers

A metallic sphere cools from $50^{\circ}C$ to $40^{\circ}C$ in $300\ s$. If the room temperature is $20^{\circ}C$, then its temperature in the next $5$ min will be

  1. $38^{\circ}C$

  2. $33.3^{\circ}C$

  3. $30^{\circ}C$

  4. $36^{\circ}C$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using Newton's Law of Cooling: (T1 - T2)/t = k(T_avg - T_env). (50 - 40)/300 = k(45 - 20) => 10/300 = k(25) => k = 1/750. For the next 300s: (40 - T)/300 = (1/750)( (40+T)/2 - 20). Solving gives T = 30 degrees Celsius.

Multiple choice physics transfer of heat applications of convection convection thermal energy transfers

In natural convection, a heated portion of a liquid moves because

  1. Its molecular motion becomes aligned

  2. Of molecular collisions within it

  3. Its density is less than that of the
    surrounding fluid

  4. Of currents of the surrounding fluid
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In natural convection, heating a fluid decreases its density, causing it to rise due to buoyancy forces, while cooler, denser fluid moves in to replace it.

Multiple choice physics transfer of heat applications of convection convection thermal energy transfers

A sphere of density d, statisfied heat s and radius r is hung by thermally insulating thread in an enclosure which is kept at a lower temperature than the sphere.The temperature of the sphere to drop at a rate which depends upon the temperature difference between the and the enclosure,If the temperature difference is $ \triangle T $ and surrounding temperature is $ T _o $ then rate of fall in temperature will be-

  1. $ \frac {4 \sigma T _o^2 \triangle T}{rdc} $

  2. $ \frac {12 \sigma T _o^2 \triangle T}{rdc} $

  3. $ \frac {12 \sigma T _o^4 \triangle T}{rdc} $

  4. $ \frac {12\sigma \triangle T}{rdc T _o^3 } $
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice physics transfer of heat applications of convection convection thermal energy transfers

The correct statement of the following:
A) Water can be boiled inside the artificial satellite by convection
B) Heavy liquid can be boiled in artificial satellite by convection
Mark correct option/s

  1. Both statements are correct

  2. Both statements are wrong

  3. A is correct but B is wrong

  4. B is correct but A is wrong
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Conduction and Convection are non-existent in space, so both the statements are wrong. 

Multiple choice physics transfer of heat applications of convection convection thermal energy transfers

It is hotter at some distance over the flames than in front of it because :

  1. air conducts heat upwards only

  2. heat is radiated upwards only

  3. convection of heat occurs upwards only

  4. heat is radiated downwards only
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Near flames, heat transfer occurs by both convection and radiation (and some conduction too).
But convection occurs only in upward direction. So, above the flame, it is hotter rather than in front of the flame.

Multiple choice physics transfer of heat applications of convection convection thermal energy transfers

Which of the following process(es) occur(s) during the convective transfer of heat within a large volume of air? 

  1. A continuous flow of warmer and cooler parts of air is established.

  2. The flow of air molecules results in flow of heat.

  3. The cooler portion of the air surrounding a warmer part exerts a buoyant force on it.

  4. As the warmer part of the air moves, it is replaced by cooler air that is subsequently warmed up.
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
Explanation

A continuous flow of warmer and cooler parts of air is established in which the air molecules are responsible for flow of heat. As the warmer air molecules move up, they are replaced bu cooler air molecules.

Multiple choice capacitance of an isolated spherical conductor capacitance of isolated bodies capacitance physics

The inductance of the oscillatory circuit of a radio station is 10 milli henry band its capacitance is $0.25 \mu F$. Taking the effect of the resistance negligible, wavelength of the broadcasted waves will be (velocity of light = $3.0  \ 10 ^4 \ m/s, \pi = 3.14$):

  1. $9,42 \times 10^4 m$

  2. $18.8 \times 10^4 m$

  3. $4.5 \times 10^4 m$

  4. $none\ of\ these$
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice capacitance of an isolated spherical conductor capacitance of isolated bodies capacitance physics

The capacitance of an air filled parallel plate capacitor is $10\times {10}^{-12}F$. The separation between the plates is doubled and the space between the plates is then filled with wax giving the capacitance a new value of $40\times {10}^{-12}F$. The dielectric constant of wax is:

  1. $12.0$

  2. $10.0$

  3. $8.0$

  4. $4.2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

${C} _{1}=\cfrac{{ \varepsilon  } _{ 0 }A}{d}$ and ${C} _{2}=\cfrac{K{ \varepsilon  } _{ 0 }A}{2d}$
$\Rightarrow$ $\cfrac{{C} _{2}}{{C} _{1}}=\cfrac{K}{2}=\cfrac{40\times {10}^{-12}}{10\times {10}^{-12}}$
$\Rightarrow$ $K=8$

Multiple choice capacitance of an isolated spherical conductor capacitance of isolated bodies capacitance physics

Each plate of parallel plate capacitor has a charge q on it. The capacitor is now connected to a battery. Now,

  1. the facing surfaces of the capacitor have equal and opposite charges

  2. the two plates of the capacitor have equal and opposite charges

  3. the battery supplies equal and opposite charges to the two plates

  4. the outer surfaces of the plates have equal charges
Reveal answer Fill a bubble to check yourself
A,C,D Correct answer