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Temperature is one of the seven fundamental quantities with dimensions [K] or [θ]. It is defined as the degree of hotness or coldness of a body.
- The natural flow of heat is from higher temperature to lower temperature.
- According to the kinetic theory of gases, temperature is a measure of the average kinetic energy of a molecule.
- Two bodies are said to be in thermal equilibrium with each other when no heat flows from one body to the other. This happens when both bodies are at the same temperature.
- Temperature is a scalar quantity and its SI unit is Kelvin (K).
- The absolute or thermodynamic temperature scale defines absolute zero as the point at which no further heat can be withdrawn from a system. This corresponds to 0 K or -273.15°C.
- The temperature of a body can be measured by a device called a thermometer.
Very Short Answers Questions [1 Mark Questions]
Ques. Why is mercury used in thermometers?
- Its volume remains constant with temperature
- It shows linear variation in volume with temperature
- Its volume is proportional to the square of the increase in temperature
- Its volume decreases with an increase in temperature
Ans. The correct answer is b. It shows linear variation in volume with temperature
Explanation: A thermometer requires a material whose physical characteristics change with temperature and can be easily connected to temperature. Because the volume of mercury increases linearly with temperature, we can construct a scale on the thermometer to indicate it.
Ques. Temperature is absolute.
- True
- False
Ans. The correct answer is b. False
Explanation: Temperature is a relative measure. For example, when we say that the temperature is 30°, it is relative to a reference like steam point and ice point.
Ques. The value of absolute zero is
- -173.15 ℃
- -273.15 ℃
- -373.15 ℃
- -473.15 ℃
Ans. The correct answer is b. -273.15 ℃
Explanation: The temperature at which a thermodynamic system has the least energy is known as absolute zero. It is equivalent to -273.15 °C on the Celsius temperature scale.
Ques. An ice cube is kept on the surface of an aluminum block and another ice cube is on the surface of a plastic block. Both blocks have the same temperature. Select the correct statement.
- Ice will melt equally fast on both blocks
- Ice will melt faster on the plastic block
- Ice will melt faster on the aluminum block
- Ice will not melt on the plastic block
Ans. The correct answer is c. Ice will melt faster on the aluminum block
Explanation: Ice melts faster on an aluminum block because it has a greater thermal conductivity than plastic and hence conducts heat more quickly.
Ques. Give a few examples of temperature sensors.
Ans. A few examples of temperature sensors are resistor temperature detectors, thermocouples, infrared sensors, and semiconductors.
Short Answers Questions [2 Marks Questions]
Ques. What is Temperature?
Ans. Temperature is a physical quantity that measures the hotness or coolness characteristic of a substance. A thermometer is used to measure temperature. It represents the kinetic energy of vibrating and colliding atoms in a substance.
Ques. What is a thermometer?
Ans. A thermometer is a device that measures temperature or the gradient of temperature. A thermometer contains two essential components: a temperature sensor, which detects changes in temperature, and a way of turning this change into a numerical number.
Ques. What is meant by absolute zero?
Ans. According to the absolute or thermodynamic temperature scale, absolute zero is defined as the point at which no further heat can be removed from a system. This is equivalent to 0 K or -273.15°C.
Ques. What is thermal expansion?
Ans. Thermal expansion is the tendency of matter to change its shape, area, volume, and density in accordance with temperature changes, but does not generally include phase transitions.
Also Read:
Long Answers Questions [3 Marks Questions]
Ques. What are the three types of temperature measuring scales?
Ans. The centigrade or Celsius (℃), Fahrenheit (℉), and Kelvin (K) are the commonly used temperature measuring scales.
To construct a scale of temperature, two fixed points are taken. The first fixed point is the freezing point (ice point) of water. It is called the lower fixed point (LFP). The second fixed point is the boiling point (steam point) of water. It is called the upper fixed point (UFP).
- Celsius scale: In this case, the lower fixed point is taken at 0° and the upper fixed point is taken at 100°. The temperature measured on this scale is all in degrees Celsius (℃).
- Fahrenheit scale: In this case, the lower fixed point is taken at 32°F and the upper fixed point is taken at 212°F. The change in temperature of 1°F corresponds to a change of less than 1° on the Celsius scale.
- Kelvin scale: The Kelvin temperature scale is also known as the thermodynamic scale. The triple point of water is selected to be zero on this scale of temperature. The temperature measured on this scale is in Kelvin (K).
Ques. What are the main influences of temperature in nature?
Ans. Temperature is related to a wide range of physical processes. Such physical properties of bodies include vapor pressure, density, solubility, electrical conductivity, state of matter, thermal conductivity, strength, etc. Other similar phenomena include
- The type and amount of thermal radiation emitted from the surface of an object.
- The range and speed at which chemical reactions take place.
- Almost every living thing is directly affected by air temperature.
- The sound speed is proportional to the absolute temperature.
Ques. In a mercury thermometer, the ice point (lower fixed point) is marked as 10° and the steam point (upper fixed point) is marked as 130°. At 40 ℃ temperature, what will this thermometer read?
Ans. Given
- Temperature on the Celsius scale, TC = 40 ℃
- LFP of the given thermometer scale = 10°
- UPF of the given thermometer scale = 130°
We know
- LFP of the Celcius scale = 0 ℃
- UFP of the Celcius scale = 100 ℃
Let T be the temperature reading of given thermometer at 40 ℃ temperature
On comparing the scale of this thermometer with the Celsius scale, we get
(TC - 0)/(100 - 0) = (T - 10)/(130 - 10)
⇒ 40/100 = (T - 10)/120
⇒ T = 58°
Very Long Answers Questions [5 Marks Questions]
Ques. What is the difference between heat and temperature?
Ans. The following are the differences between heat and temperature
| Heat | Temperature |
|---|---|
| The total energy of all molecular motion inside an object is defined as its heat. | The thermal energy or average heat of the molecules in an object is measured by temperature. |
| Heat is measured as the product of the number of atoms and the energy that each atom possesses. | Temperature is comparable to a level that determines the direction of heat flow. It is related to the rate at which the molecules inside a material move. |
| Heat has the ability to do work because it is a form of energy. | Temperature can only be used to measure the degree of heat. |
| The SI unit of heat is joule (J). | The SI unit of temperature is Kelvin (K). |
| A calorimeter is a device that measures the amount of heat in a chemical or physical process. | A device known as a thermometer is used to measure the temperature of a body. |
Ques. What are the factors that affect the temperature of a place?
Ans. The factors that affect the temperature of a place are
- Latitude: Because the earth's crust is curved, the vertical rays of the sun impact various parts of the earth's surface at different angles. Vertical rays approach the earth's surface at an angle of 90 degrees (angle of incidence) towards the poles at the equator.
- Altitude: The amount of atmosphere decreases as altitude increases, resulting in less water vapor in the air. Because the atmosphere absorbs less heat, the temperature at higher altitudes decreases.
- Ocean currents: Ocean currents are huge streams of water that move through the oceans. These occur when winds blow across the water's surface.
- Distance from the sea: The temperature of regions near the coast differs from those further inland due to a difference in the heating of land and water.
- Humidity: Humidity is the quantity of water vapor in the atmosphere, and it affects cloud cover. The larger the quantity of cloud cover, the higher the humidity. The lower the humidity, the less cloud cover.
- Cloud cover: The amount of cloud cover is larger near the equator. Cloud cover will be lower in areas of the desert when humidity is low.
- Aspect: The aspect of a slope is the direction it faces with respect to the sun. The aspect is less significant in tropical areas since the sun is high in the sky during the day. The sun has a low angle in temperate areas in winter, which affects the temperature of slopes that face north to south. In the northern hemisphere, the south-facing slope receives more solar energy and is generally warmer than the north-facing slope.
Ques. The coefficient of volume expansion of a liquid is 49 x 10-5 K-1. Calculate the fraction change in its density when the temperature is raised by 30 ℃.
Ans. When the temperature of a liquid is increased by ΔT ℃, the mass will remain unchanged while due to the thermal expansion volume will increase.
Let V0 be the initial volume, then the final volume of the liquid is given by
V = V0(1 + ℽΔT)
Where ℽ is the coefficient of volume expansion of the liquid.
Let the initial density of the liquid, ρ0 = m/V0
The final density of the liquid, ρ = m/V
⇒ ρ = m/[V0(1 + ℽΔT)]
⇒ ρ = ρ0/(1 + ℽΔT)
Fraction change in density = (ρ - ρ0)/ρ = 1 - (ρ/ρ0)
⇒ Fraction change in density = 1 - [1/(1 + γΔT)]
On substituting the values, we get
Fraction change in density = 1 - [1/(1 + 49 x 10-5 x 30)] = 1.5 x 10-2
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