Heat And Thermodynamics

Heat And Thermodynamics: Physics

Question: Ice is packed in sawdust because—

(A) Saw dust does not stick to the ice
(B) Saw dust will not get melt easily
(C) Saw dust is a good conductor of heat
(D) Saw dust is a poor conductor of heat
Ans. (D) Saw dust is a poor conductor of heat.
Explanation : Saw dust is a poor conductor of heat. Thus it does not let the atmospheric heat to pass through it and melt the ice.

Question: Therm is the unit of—
(A) Power
(B) Heat
(C) Light
(D) Distance
Ans. (B) Heat.
Explanation : Therm is the non SI unit of heat, just as celsius and fahrenheit are of temperature.

Question: Water is used in hot water bags because
(A) It is easily available
(B) It is cheap and not harmful
(C) Its specific heat is more
(D) Water can be heated easily
Ans. (C) Its specific heat is more.
Explanation : The water has high specific heat. Thus it takes more time to loose heat and get cool.

Question: Water is used in hot water bags because—
(A) It is easily available
(B) It is cheap and not harmful
(C) Its specific heat is more
(D) Water can be heated easily
Ans. (C) Its specific heat is more.
Explanation : The water has high specific heat. Thus it takes more time to loose heat and get cool.

Question: A body absorbs maximum amount of heat when it is——
(A) Black and rough
(B) Black and smooth
(C) White and rough
(D) White and smooth
Ans. (A) Black and rough .
Explanation : Best absorbers – Black & Rough surface. Best reflectors – White & Smooth surface.

Question: Heat of a reaction does not depend upon—
(A) Temperature of reaction
(B) Path by which final product is obtained
(C) Physical state of product and reactant
(D) Reaction takes place at constant pressure or constant volume.
Ans. (B) Path by which final product is obtained.                                            Explanation : The heat of reaction is a state function & it depends upon the physical condition of reactant, product, pressure and volume and does not depend on the path by which final product is obtained.

Question: In Winter season water coming out of hand pumps is hot because—
(A) In winter our body temperature remains low, so water makes us feel hot.
(B) Inside the earth temperature is more than the atmospheric temperature
(C) Due to pumping function is produced which causes heat and makes water hot
(D) Water comes out from the Earth and gains the heat from surroundings.
Ans. (B) Inside the earth temperature is more than the atmospheric temperature.
Explanation : Mud being a poor conductor of heat does not allow heat of underground water to escape out. Hence, we find it warm.

Heat And Thermodynamics : Physics

Question: Which of the following causes more burn?
(A) Boiling water
(B) Hot water
(C) Steam
(D) None of these
Ans. (C) Steam
Explanation : Steam causes more burn because it has more heat in the form of Latent Heat of Vaporization.

Question: The direction of flow of heat between any two system depends on
(A) Their specific heat
(B) Their latent heat
(C) Their individual temperature
(D) Amount of heat they contain individually.
Ans. (C) Their individual temperature.
Explanation : Heat always flows from higher temperature to lower temperature. So, direction of flow of heat always depends upon bodies individual temperatures.

Question: Due to the horizontal motion of air, transfer of heat is known as:
(A) Advection
(B) Convection
(C) Conduction
(D) Radiation
Ans. (A) Advection.
Explanation : The transfer of heat or matter by the flow of fluid horizontally is known as Advection.

Question: Burns caused by steam cause much more irritation than those caused by boiling water because—
(A) Temperature of steam is higher
(B) Steam has latent heat of vaporization
(C) Steam is a gas and engulfs the pores of body quickly
(D) Steam pierces through the pores of body quickly.
Ans. (B) Steam has latent heat of vaporization.                                 Explanation : Burns caused by steam cause much more irritation than those caused by boiling water because steam has more heat energy in the form of Latent heat of vaporization.

Question: Convection occurs in which of the following
(A) Only solids and liquids
(B) Only liquids and gases
(C) Only gases and solids
(D) Solid, liquid and gases
Ans. (B) Only liquids and gases.
Explanation : Convection is the movement of molecules in a solution (liquid, gases, plasma) according to their kinetic energy which is imparted by heat energy. It can not occur in solids. Since no molecular motion is possible in solids

Question: Which of the following liquid contains highest rate of vaporization.
(A) Kerosene oil
(B) Water
(C) Petrol
(D) Alcohol
Ans. (D) Alcohol
Explanation : Lower the boiling point, more will be the rate of vaporization. Alcohol has the lowest boiling point of all the four, hence highest rate of vaporisation.

Question: The hottest part of gas flame is known as
(A) Non- luminous zone
(B) Blue zone
(C) Luminous zone
(D) Dark zone
Ans. (A) Non- luminous zone .
Explanation : Non-Luminous zone is the hottest part of the gas flame. It is the outermost part of gas flame & hence complete combustion takes place here.

Heat And Thermodynamics : Physics

Question: Earth is a—
(A) Good reflector of heat
(B) Bad absorber of heat
(C) Good absorber and good radiator of heat
(D) Bad absorber and bad radiator of heat.
Ans. (D)Bad absorber and bad radiator of heat.
Explanation : All bad absorbers are bad radiators. Earth being a bad absorber, it is a bad radiator as well.

Question: Why are the handles of metallic teapots made of wood?
(A) Wood is a bad conductor of heat
(B) It does not cause electric shocks
(C) It makes containers look beautiful
(D) It makes containers look clean
Ans. (A) Wood is a bad conductor of heat.
Explanation : As wood is a bad conductor of heat it does not let heat to pass through it and it makes it easier to hold metallic teapots with a wooden handle,

Question: Why two thin shirts can keep us warmer than a single thick shirt in winters?
(A) shirt become thick so present permission of heat.
(B) Layer of shirt acts as a conductor of heat between two shirts.
(C) Layer of air acts as an insulating medium between two shirt.
(D) Radiation of heat doesn’t take place.
Ans. (C) Layer of air acts as an insulating medium between two shirt.

Explanation : Air trapped between two shirts act as an insulator and does not let body heat to travel out.

Question: Energy travels from sun to earth by which of the following method—
(A) Conduction
(B) Insolation
(C) Radiation
(D) Modulation
Ans. (C) Radiation.
Explanation : Radiation is the emission and propagation of energy in the form of waves or particles. The sunlight is an electromagnetic radiation it reaches earth by the process of Radiation.

Heat And Thermodynamics: Physics

Question: The characteristics invalid for heat radiation is that it travels
(A) In a straight line
(B) In all directions
(C) With the speed of light
(D) Heating the medium through which it passes.
Ans.(D)Heating the medium through which it passes.
Explanation : Heat radiations do not need any material medium for its propagation, hence no heating takes place as no medium is present.

Question: Which of the following is a good conductor of heat but bad conduction of electricity.
(A) Mica
(B) Asbestos
(C) Celluloid
(D) Paraffin wax
Ans. (A)Mica
Explanation : Mica is a good conductor of heat but bad conductor of electricity because it does not have free electrons.

Question: Which of the following has the largest value of specific heat.
(A) Glass
(B)Copper
(C) Lead
(D) Water
Ans. (D)Water
Explanation : The specific heat of water is 1 calorie/gram. The specific heat of water is higher than any other common substance.

Heat And Thermodynamics: Physics

Question: When hot water is sprinkled on a hotter glass tumbler it breaks because
(A) Glass suddenly expands
(B) Glass suddenly contracts
(C) Water evaporates
(D) Glass reacts chemically with water
Ans: (B) Glass suddenly contracts.
Explanation : On sprinkling water on hot glass tumbler it suddenly contracts. Due to this rapid contraction, it breaks.

Question: Which one of the following is an insulator?
(A) Copper
(B) Wood
(C) Mercury
(D) Aluminium
Ans. (B)Wood
Explanation : Insulators are the substances/materials which do not readily allow the passage of heat and electricity through them. Examples of insulators are glass, wood, plastic, rubber etc.

Question: Heat is transmitted from higher temperature to lower temperature through the actual motion of the molecules in—
(A) Conduction
(B) Convection
(C) Radiation
(D) Both conduction and convection
Ans. (B) Convection.

Explanation :                                     Convection – It is the transfer of energy by actual movement of a medium particles.
Conduction – The molecules excite their successive neighbours but don’t leave their position.
Radiation – The energy is transferred in the form of waves.No medium is required.

Question: Which of the following are methods of heat transfer—
(A) Convection
(B) Evaporation
(C) Revolution
(D) Thermal Expansion
Ans. (A) Convection
Explanation : Convection – It is the process of heat transfer in a gas or liquid by circulation of the currents downwards to upwards.

Question : Which of the following devices can be used to detect radiant heat—
(A) Liquid thermometer
(B) Six’s maximum and minimum thermometer
(C) Constant volume air thermometer
(D) Thermopile
Ans. (D)Thermopile
Explanation : Thermopile is a set of thermocouples arranged for measuring small quantities of radiant heat.

Question: Why white clothes keep you cooler as compared to black clothes?
(A) They absorb whole of the light
(B) They reflect the whole light
(C) Penetration of light does not occur
(D) Make the sunlight completely cool.
Ans. (B)They reflect the whole light.
Explanation : Because white clothes reflect the whole light and do not absorb any heat radiation.

Also Read: Units of Measurement.

Heat And Thermodynamics: Physics

Question: The unit of planck’s constant is—
(A) Js
(B) Js-¹
(C) Js-²
(D) Js²
Ans. (A) Js

Question: The dimensional formula of plank’s constant
(h) contains the dimension of
(A) Linear Motion
(B) Angular Momentum
(C) Energy
(D) Force
Ans. (B) Angular Momentum.

Question: When hot liquid is poured into a thick glass tumbler it cracks because glass:
(A) Is a bad conductor of heat so only inner surface expands
(B) Has high temperature coefficient of expansion
(C) Has very low specific heat
(D) Has very low temperature coefficient of expansion.
Ans. (A) Is a bad conductor of heat so only inner surface expands Explanation : Inner surface of the glass will expand more than the outer surface.

Question: A real gas can act as ideal gas at—
(A) Low pressure and High temperature
(B) High pressure and Low temperature
(C) Low temperature and High pressure
(D) High temperature and Low pressure
Ans. (A) Low pressure and High temperature.
Explanation : At low pressure and high temperature, Real gas can act as ideal gas as intermolecular force of attraction is negligible.

Question: A white and smooth surface is
(A) Good absorber and Good reflector of heat
(B) Bad absorber and Good reflector of heat
(C) Good absorber and Bad reflector of heat
(D) Bad absorber and Bad reflector of heat
Ans. (B) Bad absorber and Good reflector of heat.

Question: Outside of cooking utensils are generally left black from below because—
(A) It is difficult to clean daily
(B) Black surface is a good conductor of heat
(C) Black surface is a poor conductor of heat
(D) Black surface is a good absorber of heat
Ans. (D)Black surface is a good absorber of heat.
Explanation : Black colour absorbs all the radiations that falls on it. Hence, to supply more heat to the food in the utensil they are kept black.

Heat And Thermodynamics: Physics

Question: In a refrigerator what produces cooling?
(A) The ice which deposits on the freezer
(B) The sudden expansion of a compressed gas
(C) The evaporation of a volatile liquid
(D) None of these
Ans. (B) The sudden expansion of a compressed gas.
Explanation : Refrigerator consists of devices that Compress and expand refrigerant gas. When gas is compressed it expels heat and when it is expanded, it absorbs heat. Thereby produce cooling.

Question: In a refrigerator a cooling system should always be
(A) At the top
(B) At the bottom
(C) At the middle
(D) Can be anywhere
Ans. (A)At the top.
Explanation : Air on getting warmer rises up. This air is trapped by cooling unit on the upward side and made cool.

Question: A blackbody can absorb radiations of—
(A) Lower wavelengths only
(b) Intermediate wavelength only
(C) Higher wavelengths only
(D) All wavelengths
Ans. (D)All wavelengths.
Explanation : A blackbody is a body that absorbs all incident radiations falling on it regardless of the frequency and wavelength of the radiation.

Question: The wavelength at which the peak of intensity of black body radiation occurs.
(A) Increases with increase in temperature
(B) Decreases with increase in temperature
(C) Is the same at all temperature
(D)Doesnot follow any pattern as temperature changes
Ans.(B) Decreases with increase in temperature.
Explanation : This is according to the Wien’s displacement Law, Higher the temperature, lower is the wavelength.

Question: A cycle tyre bursts suddenly. This represents an
(A) Isothermal process
(B) Adiabatic process
(C) Isochoric process
(D) Isobaric process
Ans. (B)Adiabatic process.
Explanation : Bursting of cycle tyre is considered as an adiabatic process because it happens suddenly without any time for heat exchange.

Question: Temperature of distant luminous bodies can be determined by—
(A) Mercury Thermometers
(B) Gas Thermometers
(C) Pyrometers
(D) Colour Thermometers
Ans. (C) Pyrometers Explanation: Pyrometer is a device that measures temperature of a surface of the spectrum of thermal radiation from a distance.

Heat And Thermodynamics: Physics

Question: To measure very high temperature, we use:
(A) Mercury thermometer
(B) Platinum Resistance thermometer
(C) Thermoelectric Pyrometer
(D) None of these
Ans. (C)Thermoelectric Pyrometer

Question: The minimum temperature is measured by—
(A) Alcohol Thermometer
(B) Thermometer
(CMaximum Reading Thermometer
(D) Minimum Reading Thermometer
Ans. (A)Alcohol Thermometer .

Question: Temperature inversion is:
(A) Positive lapse rate
(B) Negative lapse rate
(C) Neutral condition
(D) None of these
Ans. (B) Negative lapse rate.

Question: Absolute zero is defined as the temperature
(A) At which all molecular motion ceases
(B) At which water boils at 298Bk
(C) At which liquid helium boils
(D) At which volume becomes zero
Ans. (A)At which all molecular motion ceases.
Explanation : Absolute zero is 0 K. It is the lowest possible temperature. At 0 K, all molecular motion cease and molecules have minimum kinetic energy.

Question: In which form is the supplied heat energy stored during change in temperature of substance?
(A) Heat Energy
(B) Kinetic Energy
(C) Potential energy
(D) Both kinetic and potential energy
Ans. (B)Kinetic Energy.
Explanation: On supplying heat, atoms of the su bstance begin to vibrate due to increased kinetic energy.

Question: Gas thermometers are more sensitive than iquid thermometer because the gases—
(A) Have larger coefficient of expansion
(B) Are lighter
(C) Have low specific heat
(D) Have high specific heat
Ans. (A)
Explanation : Gas molecules have larger coefficient of expansion than liquid. Hence for a small amount of heat, they show greater volatility.

Question: What changes will happen to a bowl of ice and water kept at exactly zero degree Celsius.
(A) All ice will melt
(B) All water will become ice
(C) No change will happen
(D) Only some ice will melt
Ans. (C) No change will happen.
Explanation : Heat flows from a body at a higher temperature to a body at lower temperature. As both ice and water are at 0°C. Therefore, no heat flow will take place, hence no change will happen.

Question: The temperature of boiling water in a steam engine may be high because—
(A) There are dissolved substances in water
(B) There is low pressure inside the boiler
(C) There is high pressure inside the boiler
(D) The fire is at very high temperature
Ans. (C)There is high pressure inside the boiler.
Explanation : The higher the pressure inside a boiler, the higher the temperature of boiling water.