Heat Transfer — Set 1
Physics · ऊष्मा स्थानांतरण · Questions 1–10 of 50
Which mode of heat transfer can occur through vacuum?
Correct Answer: B. Radiation
Radiation transfers heat by electromagnetic waves, so it does not need a material medium. Conduction and convection need matter to pass energy. The Sun warms Earth mainly by radiation.
Heat transfer due to bulk motion of a fluid is called?
Correct Answer: A. Convection
Convection happens when heat is carried by moving fluid. Warm fluid becomes less dense and rises while cooler fluid sinks. Convection currents are common in water and air.
Which material is generally the best conductor of heat?
Correct Answer: C. Copper
Copper conducts heat very well because it has many free electrons. Insulators like wood and rubber resist heat flow strongly. Metals are generally good thermal conductors.
The SI unit of thermal conductivity is?
Correct Answer: A. W m⁻¹ K⁻¹
Thermal conductivity is measured in W m⁻¹ K⁻¹ in SI units. It tells how easily heat flows through a material. A larger value means faster conduction for the same conditions.
In conduction, heat flows from?
Correct Answer: A. higher temperature to lower temperature
Conduction transfers heat from a region of higher temperature to lower temperature. It occurs due to particle collisions and electron motion in solids. Heat flow stops when temperatures become equal.
Which of the following is mainly a convection phenomenon?
Correct Answer: B. Heat from the Sun reaching Earth
Sea breeze forms due to convection in air caused by uneven heating of land and sea. Warm air over land rises and cooler air from sea moves in. Conduction mainly occurs in solids, and radiation works through vacuum.
A shiny metal surface is a poor?
Correct Answer: B. absorber of sound
A shiny surface is a poor emitter of thermal radiation. It reflects radiation well and emits less compared to a black surface. Dull black surfaces are good absorbers and emitters.
Which surface is generally the best absorber of heat radiation?
Correct Answer: B. Dull black surface
A dull black surface absorbs heat radiation most effectively. Shiny and light-colored surfaces reflect more radiation. This is why solar cookers often use black interiors.
Which statement about convection in liquids is correct?
Correct Answer: C. Convection is strongest in solids
Convection requires the motion of a fluid, so it occurs in liquids and gases. Heating makes the fluid less dense and it rises. Convection is not the main heat transfer method in solids.
Why do birds often spread their wings in sunlight?
Correct Answer: A. To increase radiation absorption
Spreading wings increases the area exposed to sunlight, increasing heat gained by radiation. Radiation transfer depends strongly on surface area and exposure. Dark feathers can absorb radiation more effectively.