Heat Online Test 9th Science Lesson 7 Questions in English

Sources of heat
1. Sun
2. Combustion (Burning)
3. Friction
4. Electricity

We can generate heat by rubbing two surfaces of some substances. In the past people used to rub two stones together to light fire.

When electric current flows through a conductor, heat energy is produced. The water heater, iron box, electric kettle etc., work on this principle.

Heat is not a matter. It doesn’t occupy space. It has no weight. Like light, sound and electricity, heat is a form of energy.

Molecules in objects are constantly vibrating or moving inside objects. We cannot see that movement with our naked eye. When we heat the object this vibration and movement of molecules increases and temperature of the object also increases.

Heat is the total kinetic energy of constituent particles of objects. SI Unit of Heat is joule. The unit calorie is also used.

Heat is the total kinetic energy of constituent particles of objects. SI Unit of Heat is joule. The unit calorie is also used.

Heat is the total kinetic energy of constituent particles of objects. SI Unit of Heat is joule. The unit calorie is also used.

Measuring temperature by touching is not correct. Thermometers are used to measure temperature accurately and quantitatively.

The measurement of warmness or coldness of a substance is known as its Temperature. SI unit of temperature is kelvin. Celsius and Fahrenheit are the other units used. Celsius is called as Centigrade as well.

SI unit of temperature is kelvin. Celsius and Fahrenheit are the other units used. Celsius is called as Centigrade as well.

SI unit of temperature is kelvin. Celsius and Fahrenheit are the other units used. Celsius is called as Centigrade as well.

SI unit of temperature is kelvin. Celsius and Fahrenheit are the other units used. Celsius is called as Centigrade as well. It determines the direction of flow of heat when two bodies are placed in contact.

Normally, the room temperature of water is approximately 30o C. When we heat water, its temperature raises and it boils at 100oC. If we cool the water, it freezes at 0o C.

Normally, the room temperature of water is approximately 30o C. When we heat water, its temperature raises and it boils at 100o C. If we cool the water, it freezes at 0o C.

The minus sign (–) is used when the temperature falls below the freezing point of water, which is 0o C. If water becomes ice at 0o C, you can imagine how cold – 89o C would be. Our normal body temperature is 37o C. Our body feels cool if the air temperature is around 15 to 20 degree Celsius.

The thermometer should not touch the vessel in which the water is being heated. Otherwise the thermometer will be broken at high temperature. The minus sign (–) is used when the temperature falls below the freezing point of water, which is 0o C. If water becomes ice at 0o C, you can imagine how cold – 89o C would be. Our normal body temperature is 37o C. Our body feels cool if the air temperature is around 15 to 20 degree Celsius.

The minus sign (–) is used when the temperature falls below the freezing point of water, which is 0o C. If water becomes ice at 0o C, you can imagine how cold – 89o C would be. Our normal body temperature is 37o C. Our body feels cool if the air temperature is around 15 to 20 degree Celsius.

Heat and temperature are not the same thing, they in fact mean two different things. Heat measures the total Kinetic Energy of the molecules in the substance.

Temperature is related to how fast the atoms or molecules move or vibrate within the substance.

Temperature measures the average kinetic energy of molecules. Heat measures the total Kinetic Energy of the molecules in the substance.

Temperature is related to how fast the atoms or molecules move or vibrate within the substance. Heat not only depends on the temperature of the substance but also depends on how many molecules are there in the object.

Total heat is measured by calorie, the amount of heat needed to raise one gram of water by one degree centigrade.

Water ‘flows’ when there is a difference in the ‘levels’ of water in different places. It does not matter if there is more water in one place or another.

Water ‘flows’ when there is a difference in the ‘levels’ of water in different places. It does not matter if there is more water in one place or another. Water from a puddle can fl ow into a reservoir or the other way around.

The ‘temperature’ of an object is like the water level – it determines the direction in which ‘heat’ will flow. Heat energy flows from higher temperature to lower temperature.

Two objects are said to be in thermal contact if they can exchange heat energy. Thermal equilibrium exists when two objects in thermal contact no longer affect each other’s temperature.

Most substances expand when heated and contract when cooled. The change in length / area or volume (due to contraction / expansion) is directly related to temperature change.

Most substances expand when heated and contract when cooled. The change in length / area or volume (due to contraction / expansion) is directly related to temperature change.

Most substances expand when heated and contract when cooled. The change in length / area or volume (due to contraction / expansion) is directly related to temperature change.

The expansion of a substance on heating is called, the thermal expansion of that substance.

A solid has a definite shape, so when a solid is heated, it expands in all directions i.e., in length, area and volume, all increase on heating.

The expansion in length is called linear expansion and the expansion in volume is called cubical expansion.

The expansion in length is called linear expansion and the expansion in volume is called cubical expansion.

A small gap is left between two lengths of the railway line to avoid the track resentment due to the heat expansion of metal.

The diameter of the iron ring is slightly less than that of the wooden wheel. Therefore, it cannot be easily slipped on from the rim of wooden wheel.

The iron ring is, therefore, fi rst heated to a higher temperature so that it expands in size and the hot ring is then easily slipped over to the rim of the wooden wheel. Cold water is now poured on the iron ring so that it contracts in size and holds the wooden wheel tightly.

Rivets are used to join two steel plates together. Hot rivet is driven through the hole in the plates. One end of the rivet is hammered to form a new rivet head. When cooled, the rivet will contract and hold the two plates tightly together.

Rivets are used to join two steel plates together. Hot rivet is driven through the hole in the plates. One end of the rivet is hammered to form a new rivet head. When cooled, the rivet will contract and hold the two plates tightly together.

Glass is a poor conductor of heat. When hot liquid is poured into the tumbler, the inner surface of the tumbler becomes hot and expands while the outer surface remains at the room temperature and does not expand. Due to this unequal expansion, the tumbler cracks.

Glass is a poor conductor of heat. When hot liquid is poured into the tumbler, the inner surface of the tumbler becomes hot and expands while the outer surface remains at the room temperature and does not expand. Due to this unequal expansion, the tumbler cracks.

Glass is a poor conductor of heat. When hot liquid is poured into the tumbler, the inner surface of the tumbler becomes hot and expands while the outer surface remains at the room temperature and does not expand. Due to this unequal expansion, the tumbler cracks.

Electric wires between electric posts contract on cold days and sag in summers. To solve this problem, we leave wires slack so that they are free to change length

Electric wires between electric posts contract on cold days and sag in summers. To solve this problem, we leave wires slack so that they are free to change length.

Glassware used in kitchen and laboratory are generally made up of Borosilicate glass (pyrex glass). The reason is that the Borosilicate glass do not expand much on being heated and therefore they do not crack.

Glassware used in kitchen and laboratory are generally made up of Borosilicate glass (pyrex glass). The reason is that the Borosilicate glass do not expand much on being heated and therefore they do not crack.

One calorie heat energy is needed to raise the temperature of the water from 30o C to 31o C.

Temperature measures the average kinetic energy of molecules. Heat measures the total Kinetic Energy of the molecules in the substance.