Tag: physics

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Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

The reason for providing copper bottoms in steel pans is :

  1. aesthet, carly looks good

  2. that copper is better conductor than steel

  3. that copper is not a good conductor than steel

  4. None of the above

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Copper bottoms are provided in steel pans because copper is better conductor of heat than steel.

Thermal conductivity of copper is highest ($38600w/mK$) while that of steel is lowest ($1245w/mK$).

Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

Four rods of same material but with different radii and lengths are used to connect two reservoirs of heat with the same temperature difference. Which one will conduct more heat

  1. r=1 cm, 1=1 cm

  2. r=1 cm, 1= 2 cm
  3. r= 1 cm, $1=\frac{1}{2}m$
  4. $r=\frac{1}{2}cm$, $1=\frac{1}{2}m$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Heat conduction rate H = k*A*(delta T)/L. Since material and delta T are constant, H is proportional to A/L, or (r^2)/L. Calculating r^2/L for each: A) 1/1=1, B) 1/2=0.5, C) 1/0.5=2, D) 0.25/0.5=0.5. Option C gives the highest value.

Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

What will be the conductivity of pure silicon crystal at 300 K temperature if  electron cottoer pair at this temperature is $ 1.072 \times 10^{10} /cm^3 $ and $ \mu _n = 1350 cn^2 /V-s and \mu _p = 480 cm^2/ V-s $ ?

  1. $ 3.14 \times 10^{-4} mho /cm $
  2. $ 3.14 \times 10^{-5} mho /cm $
  3. $ 3.14 \times 10^{-6} mho /cm $
  4. $ 3.14 \times 10^{3} mho /cm $
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

The heat capacity of a body depends on 

  1. the heat given

  2. the temperature rasied

  3. the mass of the body

  4. the material of he body.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Heat capacity (C) is defined as the amount of heat required to raise the temperature of a body by one degree. It is given by C = m * c, where m is the mass and c is the specific heat capacity of the material.

Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

In a steady state of thermal conduction, temperature of the ends $A$ and $B$ of a $20cm$ long rod are $100^oC$ and $0^oC$, respectively. What will be the temperature of the rod at a distance of $6cm$ from the end $A$ of the rod?

  1. $-30^oC$
  2. $70^oC$
  3. $5^oC$

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In steady state, the temperature gradient is linear. Temperature T(x) = T_A - (T_A - T_B) * (x / L). T(6) = 100 - (100 - 0) * (6 / 20) = 100 - 100 * 0.3 = 100 - 30 = 70 degrees Celsius.

Multiple choice physics sound and noise musical sound and scale pleasant, unpleasant sounds and noise pollution sound noise and pollution

While travelling by train, when the train passes through the tunnel, why does our ear aches ?

  1. atmospheric pressure

  2. tunnel pressure

  3. water pressure

  4. None of the above

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When a train enters a tunnel, it compresses the air in front of it like a piston. Unlike outside air, air in a tunnel can’t be simply pushed aside—the tunnel walls are in the way. Some of the air is pushed forward, all the way down to the tunnel’s other end, but most of it rushes through the narrow space between the train and the tunnel walls, filling in the area behind the train. Being forced into this narrow space makes the air rush faster, exactly as water speeds up at the base of a funnel. In fact, this tunnel air can rush backward much faster than the train’s forward speed. his fast moving air creates a kind of suction on the train, lowering the air pressure inside and making your ears go pop. It cause ear aches

Hence, due to sudden increase and decrease pressure inside tunnel, aches occur in ear