Chapter 7: Thermal Properties of MatterMCQs with Answers
All 24 MCQs of 9th Class Physics Chapter 7, Thermal Properties of Matter, with answers and the reason each option is right or wrong: the 11 textbook exercise MCQs plus 13 more board-style MCQs. Punjab Board new syllabus.
Try each one first: tap an option to check it, then read the reasoning and why the others are wrong.
A note about the questions
The wording follows published solved exercises and every answer was re-checked by hand, so the wording or the order of options may differ slightly from your print.
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Set A: Textbook exercise 11 MCQs
The multiple-choice questions at the end of Chapter 7 in your book, in the book's option order.
Q7.1Kinetic Molecular Theory
How do the molecules in a solid behave?
Answer(b) vibrate about their mean positions
Step by step
In a solid the forces between molecules are very strong.
The molecules cannot leave their places, so they only vibrate about them.
Why the others are wrong
(a) random motion from place to place is how gas molecules move.
(c) molecules of a solid do not rotate freely.
(d) heat spreading through a solid does not mean its molecules travel along it.
Remember
Solid: fixed place, only vibration.
Q7.2Kinetic Molecular Theory
What type of motion is of the molecules in a gas?
Answer(b) random motion
Step by step
Gas molecules are far apart, with very weak forces between them.
They move in every direction and keep changing direction at collisions: random motion.
Why the others are wrong
(a) each molecule moves straight only between collisions; the overall motion is random.
(c) vibration about a fixed place is the motion in a solid.
(d) rotation alone does not describe the motion of gas molecules.
Remember
Gas: random, in all directions.
Q7.3Temperature and Heat
Temperature of a substance is:
Answer(c) degree of hotness or coldness
Step by step
Temperature tells how hot or cold a body is.
It does not depend on how much of the substance there is.
Why the others are wrong
(a) a body does not "contain" heat; heat is energy in transit.
(b) a cup and a bucket of boiling water have the same temperature.
(d) temperature depends on the average kinetic energy, not the spacing.
Remember
Temperature = how hot, not how much.
Q7.4Temperature and Heat
Heat is the:
Answer(d) the energy in transit
Step by step
Energy stored in the molecules is internal energy.
Only while it flows because of a temperature difference is it called heat.
Why the others are wrong
(a) that is part of the internal energy.
(b) internal energy is stored in a body; heat is energy moving between bodies.
(c) heat is not defined as work done by molecules.
Remember
Heat flows; internal energy is stored.
Q7.5Temperature Scales
In Kelvin scale, the temperature corresponding to the melting point of ice is:
Answer(d) +273
Step by step
Melting point of ice = 0 °C.
T(K) = 0 + 273 = 273 K.
Why the others are wrong
(a) 0 K is absolute zero, far colder than ice.
(b) 32 is the ice point on the Fahrenheit scale.
(c) −273 °C is absolute zero on the Celsius scale; the Kelvin scale has no negative values.
Remember
Ice point: 0 °C = 32 °F = 273 K.
Q7.6Temperature Scales
The temperature which has the same value on the Celsius and Fahrenheit scales is:
Answer(a) −40
Step by step
T = 1.8T + 32.
−0.8T = 32.
T = −40, so −40 °C = −40 °F.
Why the others are wrong
(b) 40 °C is 104 °F.
(c) 45 °C is 113 °F.
(d) −45 °C is −49 °F.
Remember
−40 is the crossing point.
Q7.7Thermometers
Which one is a better choice for a liquid-in-glass thermometer? A liquid that:
Answer(c) expands linearly
Step by step
Equal temperature rises must give equal lengths of thread.
That needs a liquid that expands linearly (uniformly).
Why the others are wrong
(a) a colourless liquid is hard to see; it must be visible.
(b) it must be a good conductor so it responds quickly.
(d) a liquid that wets the glass sticks to the tube and spoils the reading.
Remember
Good thermometric liquid: linear, visible, good conductor, does not wet glass.
Q7.8Thermometers
One disadvantage of using alcohol in a liquid-in-glass thermometer is that:
Answer(c) it wets the glass tube
Step by step
Large expansivity: an advantage (more sensitive).
Low freezing point: an advantage (measures very low temperatures).
Linear expansion: an advantage.
Wetting the glass: the disadvantage.
Why the others are wrong
(a) large expansivity makes the thermometer more sensitive, an advantage.
(b) a low freezing point lets it work in very cold places, an advantage.
(d) linear expansion is an advantage.
Remember
Ask "is this good or bad?" for each option.
Q7.9Thermometers
Water is not used as a thermometric liquid mainly because it:
Answer(c) has non-linear expansion
Step by step
Water expands irregularly (it contracts from 0 °C to 4 °C).
So a scale with equal divisions would give wrong readings.
Why the others are wrong
(a) true, but colour could be added; it is not the main reason.
(b) true, but not the main reason.
(d) a small range is a drawback, but not the main reason.
Remember
Water is irregular: the main reason.
Q7.10Sensitivity, Range and Linearity
A thermometer has a narrow capillary tube so that it:
Answer(c) gives a large change for a given temperature rise
Step by step
Increase in volume = area of bore × length moved.
A small area means a large length for the same volume change.
Why the others are wrong
(a) a quick response comes from a thin-walled bulb and a little liquid.
(b) holding the maximum reading is the job of the constriction in a clinical thermometer.
(d) a narrow bore actually limits the range for a given length of tube.
Remember
Narrow bore = long movement = sensitive.
Q7.11Thermometers
Which thermometer is most suitable for recording a rapidly varying temperature?
Answer(a) thermocouple thermometer
Step by step
A liquid-in-glass thermometer must first heat its glass and liquid: slow.
A thermocouple junction is very small: very fast response.
Why the others are wrong
(b) the glass and mercury take time to heat up.
(c) alcohol in glass is also slow.
(d) a clinical thermometer is slow and holds its reading on purpose.
Remember
Fast-changing temperature: thermocouple.
Set B: More MCQs from this chapter 13 MCQs
Extra questions on the same ideas, of the kind set in board papers and class tests.
QB1Kinetic Molecular Theory
Plasma is called the fourth state of matter. It consists of:
Answer(b) positive ions and free electrons
Step by step
Very high temperatures knock electrons out of atoms.
What remains is a mixture of positive ions and free electrons: plasma.
Why the others are wrong
(a) that is an ordinary gas.
(c) plasma has electrons too.
(d) tightly packed atoms describe a solid.
Remember
Plasma = ionised gas.
QB2Kinetic Molecular Theory
The Sun and other stars are made of matter in which state?
Answer(d) plasma
Step by step
Temperatures of millions of degrees ionise the atoms.
Ionised gas is plasma.
Why the others are wrong
(a) the Sun is far too hot to be solid.
(b) it is far too hot to be liquid.
(c) its gas is ionised, which makes it plasma.
Remember
Stars, lightning, neon signs: plasma.
QB3Temperature and Heat
The sum of the kinetic and potential energies of all the molecules of a body is called its:
Answer(c) internal energy
Step by step
Molecules move: kinetic energy.
They attract each other: potential energy.
The total is internal energy.
Why the others are wrong
(a) heat is energy in transit, not stored.
(b) temperature relates to the average kinetic energy only.
(d) thermal equilibrium is the state of equal temperatures.
Remember
Stored inside = internal energy.
QB4Temperature and Heat
Heat always flows from:
Answer(b) a body at higher temperature to one at lower temperature
Step by step
Heat flows because of a temperature difference.
It stops when the temperatures become equal (thermal equilibrium).
Why the others are wrong
(a) mass does not decide the direction.
(c) a large cold lake has more internal energy than a hot cup, yet heat flows from the cup.
(d) the state of matter does not decide it.
Remember
Hot to cold, always.
QB5Temperature Scales
The value of absolute zero on the Celsius scale is:
Answer(c) −273.15 °C
Step by step
0 K = −273.15 °C.
Why the others are wrong
(a) 0 °C is the ice point.
(b) not a special point.
(d) 373 is the steam point on the Kelvin scale.
Remember
0 K = −273 °C.
QB6Temperature Scales
On the Fahrenheit scale, the space between the ice point and the steam point is divided into:
Answer(b) 180 equal parts
Step by step
212 − 32 = 180.
Why the others are wrong
(a) 100 parts is Celsius or Kelvin.
(c) 212 is the steam point, not the number of parts.
(d) 273 is the Kelvin ice point.
Remember
F: 180 parts; C and K: 100 parts.
QB7Temperature Scales
A temperature of 300 K on the Celsius scale is:
Answer(a) 27 °C
Step by step
T(°C) = T(K) − 273.
300 − 273 = 27 °C.
Why the others are wrong
(b) it adds 273 instead of subtracting.
(c) the sign is wrong.
(d) 30 °C is 303 K.
Remember
K to °C: subtract 273.
QB8Temperature Scales
A temperature of 50 °C on the Fahrenheit scale is:
Answer(b) 122 °F
Step by step
T(F) = 1.8 T(C) + 32.
1.8 × 50 = 90; 90 + 32 = 122 °F.
Why the others are wrong
(a) it forgets to add 32.
(c) it adds 32 to 50 instead of to 90.
(d) that comes from the reverse formula.
Remember
Multiply by 1.8 first, then add 32.
QB9Temperature Scales
A change of temperature of 1 K is equal to a change of:
Answer(a) 1 °C
Step by step
Celsius: 0 to 100 (100 parts). Kelvin: 273 to 373 (100 parts).
So a step of 1 K = a step of 1 °C.
Why the others are wrong
(b) 1 °C = 1.8 °F, not 1.8 °C.
(c) 273 is the offset, not the step.
(d) a Fahrenheit degree is smaller.
Remember
Same step size, different starting point.
QB10Thermometers
The usual range of a clinical thermometer is:
Answer(b) 35 °C to 42 °C
Step by step
Normal body temperature is 37 °C.
A small range lets the scale be marked finely.
Why the others are wrong
(a) that is a laboratory thermometer.
(c) that is a general laboratory range.
(d) that is the range over which mercury stays liquid.
Remember
Clinical: about 35–42 °C.
QB11Thermometers
The narrow constriction (kink) near the bulb of a clinical thermometer:
Answer(b) stops the mercury falling back, so the reading stays after the thermometer is removed
Step by step
Mercury expands past the constriction as it warms.
On cooling, the thread breaks at the constriction and stays up.
Why the others are wrong
(a) it does not change the expansion.
(c) it has nothing to do with the range.
(d) it does not cool the bulb.
Remember
Constriction = holds the reading.
QB12Thermometers
Mercury freezes at −39 °C. For measuring temperatures in very cold regions (below −39 °C) we use a thermometer filled with:
Answer(c) alcohol
Step by step
Mercury freezes at −39 °C.
Alcohol freezes at about −112 °C.
Why the others are wrong
(a) water freezes at 0 °C.
(b) mercury freezes at −39 °C.
(d) oil is not used as a thermometric liquid.
Remember
Very cold: alcohol.
QB13Thermometers
A thermocouple thermometer works because:
Answer(b) a current flows when the two junctions of two different metals are at different temperatures
Step by step
Join copper and iron wires at two ends.
Keep one junction cold and put the other in the hot body.
The galvanometer current gives the temperature.
Why the others are wrong
(a) that is a liquid-in-glass thermometer.
(c) that is a gas thermometer.
(d) expansion of a solid is not the principle.
Remember
Thermocouple: two metals, two junctions, a current.
