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CBSE Questions for Class 7 Physics Heat Quiz 3 - MCQExams.com
CBSE
Class 7 Physics
Heat
Quiz 3
The hotness of an object is determined by its ...............
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Temperature
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Specific Heat Capacity
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Radiation
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Conduction
Explanation
1. The hotness of an object is determined by its temperature.
2. Specific heat capacity
is defined as the amount of heat required to raise the temperature of 1 kilogram of a substance by 1 kelvin
3. R
adiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium.
4.
Conduction
is the process by which heat energy is transmitted through collisions between neighboring atoms or molecules.
Temperature of boiling water cannot be measured by a ________ thermometer.
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Clinical thermometer
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Laboratory thermometer
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Both $$A and B
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None of these
Explanation
The temperature of boiling water cannot be measured by a Clinical thermometer because the range of clinical thermometer varies between only $$35^\circ C$$ to $$42^\circ C.$$
Essential requirement to propagation Heat energy:
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no medium
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gaseous medium
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solid medium
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liquid medium
Explanation
Heat energy can propagate by radiation, which is a mode of propagation of heat energy. Radiation doesn't require any medium hence heat energy essentially requires no medium for propagation .
Transmission of heat by the movement of heated particles is called
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Conduction
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Convection
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Radiation
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Regelation
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Expansion
Explanation
Convection is a mode of heat transfer in which the molecules near the heat source get heated up, expand, become less dense, and rise upwards. But the relatively colder molecules sink to the bottom and eventually get heated up. Thus the transmission of heat by the movement of heated particles is called convection.
An instrument used to measure high temperature is
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Pyrheliometer
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Pyrometer
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Tachometer
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Pyknometer
Explanation
An instrument used to measure high temperature is Pyrometer.
A pyrometer is used to measure high temperatures in the furnace. It is a type of remote sensing thermometer used to measure temperature for the surface.
Pyrheliometers measure only the sunlight from a small area around the sun.
A tachometer is an instrument measuring the rotation speed of a shaft or disk.
A gas pycnometer is a laboratory device used for measuring the density or, more accurately, the volume of solids.
Conduction cannot take place in:
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Copper
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Iron
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Aluminium
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Vacuum
Explanation
A medium is required for conduction to take place. Since vacuum does not have a medium, conduction does not take place.
In convection currents, heat is transferred upwards
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horizontally
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diagonally
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vertically
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none of these
Explanation
Convection is mode of heat transfer in which medium particles moves while transferring the heat. ex- Process of Heating of water; water molecules near the bottom areas of container takes heat and rise the top at the same time another water molecules come down. this goes continuously and water get warm. this phenomena of heat transfer is called convection heat transfer. and heat current flow from bottom to top ie vertically upward.
By the process of convection the transfer of heat is always-
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upwards
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downwards
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sideways
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in all possible directions
Explanation
By the process of convection the transfer of heat is always upwards.
Liquid and gases are bad conductors of heat. They are heated mainly by the process of convection. Solids can't be heated by the process of convection, In the process of convection the transfer of heat is always vertically upwards.
The continuous movement of a fluid when heated is called :
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convectional current
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conduction current
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electric current
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magnetic current
Explanation
Convection is a process of transfer of heat through a fluid (liquid or gas) caused by molecular motion. When the particles of the medium get heated and move up and the cooler particles come down to take their place, then they get heated and move up, and a continuous
movement of fluid takes place as long as the source of heat is there, then its called a convectional current.
In which mode of transfer of heat molecules pass on heat energy to neighbouring molecules without actually moving from their positions?
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convection
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radiation
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conduction
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none of these
Explanation
Conduction is the mode of heat transfer of heat molecules pass on heat energy to neighbouring molecules without actually moving from their positions.
Conduction is the transfer of heat from one substance to another by direct contact without mixing of masses.
Which of the following is a good conductor of heat?
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Plastic
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Mercury
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Water
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Alcohol
Explanation
Mercury is categorized under metasl and we know that metals conduct heat better than non-metals.
So mercury is the answer.
During day time the air becomes warm due to the process of-
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conduction
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convection
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radiation
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expansion
Explanation
During day time the air becomes warm due to process of radiation.
Heat transfer through radiation takes place in form of electromagnetic waves mainly in infrared region. Radiation emitted by a body is consequence of thermal agitation of its composing molecules.
Convection cannot take place in_______
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solids
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liquids
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gases
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None of the above
Explanation
Convection can't take place in solids.
Convection is transfer of heat through fluid (liquid or gas) caused by molecular motion.
The rate at which a body radiates heat depends on-
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its temperature
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its colour
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its nature (dull or shiny)
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all of these
Explanation
The rate at which body radiates depends upon its nature (shiny or dull).
Nature represents emmisivity of body (radiation emittence) and absorptivity of medium (radiation absorptance of medium compared to black body).
The air becomes heated by
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Conduction
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Convection
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Radiation
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Expansion
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Diffusion
Explanation
Convection is a mode of heat transfer where the molecules near the heat source get heated up. They absorb energy, expand, become less dense, and rise upwards.
On the other hand, the relatively colder molecules sink to the bottom and eventually get heated up again. Thus air gets heated by convection.
Mercury is a
good
conductor of heat. State true or false.
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True
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False
Explanation
Mercury is a good conductor of heat. (True)
Thermal conductivity of mercury is high. This is the fact why it has been used in classical thermometers for measuring temperature.
State whether given statement is True or False
The heat coming from the sun travels by convection
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True
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False
Explanation
Heat from Sun reaches us by the process of radiation. As we know radiation do not need any material medium for heat transfer. It takes place in the form of electromagnetic radiations. In space (where there is Sun) there is no atmosphere, no medium, so convection can't take place. By radiation only heat can be transmitted by Sun to earth.
Convection currents are possible in solids
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True
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False
Explanation
No, convection currents are not possible in solid. Convection is heat transfer by mass motion of a fluid such as air or water. Convection does not occurs in solid because the particles within are tightly packed to facilitate the process. Convection requires actual movement between particles within a substance.
State whether given statement is True or False :
Mud houses are hot in summer and cold in winter.
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True
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False
Explanation
Mud houses have thatched roofs. The insulating effect of the thatch prevents heat from getting in very quickly which makes the houses cool during summer, and also it prevents the heat from getting out very quickly during winters, thus making the houses warm during winter.
Secondly, mud houses are made up of mud, which has large pores. As evaporation causes cooling, mud houses feel cooler during summer.
This is why "mud houses are hot in summer and cold in winter" is a FALSE statement.
Heat transfer through radiation cannot take place in vacuum. True or false
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True
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False
Explanation
False
Radiation can take place in vacuum too as radiation do not require any material medium for transfer of heat. It takes place by electromagnetic waves.
Air is a good conductor of heat. True or false.
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True
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False
Explanation
False
Air is bad conductor of heat. It is due to the air trapped between the cotton molecules which gives warmth on taking quilt in winter It is due to air molecules trapped between wool fabrics which provide warmth to body during winter season.
State whether given statement is True or False
Heat from the sun reaches us by the process of convection
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True
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False
Explanation
Heat from the Sun reaches is by the process of radiation. As we know radiation do not need any material medium for heat transfer. It takes place in the form of electromagnetic radiations. In space (where there is Sun) there is no atmosphere, no medium; so convection can't take place. By radiation only heat can be transmitted by Sun to Earth.
Wearing black clothes in summer is more preferable. True or false.
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True
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False
Explanation
False
Wearing black clothes in summer is not preferable as during summer there is more heat present in the atmosphere and black clothes absorb more heat comparatively. So, black clothes are not preferable during summer.
State whether given statement is True or False.
Iron is a better conductor of heat than copper.
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True
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False
Explanation
Thermal conductivity of copper is greater than that of iron.
Select the odd one out w.r.t. conduction of heat (wood, mica, plastic, iron)
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iron
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plastic
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wood
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mica
Explanation
Iron is a good conductor of heat rest all are insulators
Select the odd one out w.r.t. conduction of heat
(wood, paper, plastic, silver)
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Silver
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Wood
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Paper
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Plastic
Explanation
Silver is a good conductor of heat rest are bad conductors of heat.
Select the odd one out (conduction, convection, radiation,
expansion)
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conduction
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convection
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radiation
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expansion
Explanation
All are modes of heat transfer while expansion is an effect of heat
Select the odd one out with respect to the conduction of heat.
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Cork
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Gold
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Copper
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Mercury
Explanation
The materials which allow heat to pass through them easily are called conductors of heat. For example, gold, copper, and mercury.
The materials which do not allow heat to pass through them easily are called insulators. For example, cork.
Select the odd one out w.r.t. conduction of heat.
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asbestos
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gold
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silver
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copper
Explanation
Asbestos is an insulator and rest are metals which are good conductors of heat.
State True or False:
Air conducts heat.
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True
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False
Explanation
False, air does not conduct heat.
Air is a poor conductor of heat because its molecules are not in continuous contact with each other.
Air molecules are too far to disperse heat energy to each other efficiently. Heat is conducted by molecules and atoms that are very closely bonded together and vibrating at high frequency.
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