What is Heat? Class 10| SEE Physics notes

Heat:

Definition: The heat is a form of energy which produces the sensation of warmth (Hotness). It is measured in Joule(J).

Temperature:

Definition: The degree of hotness or coldness of a body is called temperature.Its SI unit is Kelvin (K).

A relation between Joule and Calorie:

2.4 Joule=1 calories

Calorie: The amount of heat used to raise the temperature of a 1gm substance by 1°C is called Calorie.

A relationship among Celcius, Fahrenheit, and Kelvin:

C-0°/100 = F-32°/180 = K-273°/100
or, C-0°/10 = F-32°/18 = K-273°/10

Source of energy: The largest source of energy is called Sun. It radiates heat and light by nuclear.

A principle of Nuclear fusion: E=mc²

Specific heat capacity (S):

Definition: The amount of heat required to raise the temperature of a 1kg substance by 1°C is called Specific heat capacity (S).

Q∝m — (a)
Q∝ ΔE — (b)
From (a) and (b)
Q∝ Δt
or, Q=smΔt

Where,
Q= Amount of heat (Joule)
m= Mass of substance (Kg)
Δt= Difference in temperature (C°).
S= Specific heat capacity.

S= Q/mΔt
= Joule/Kg°C
=J/kg°C

Factors on which Specific heat capacity depends:

• S∝Q
• S∝1/m
• S∝1/Δt

Read:

• Energy for SEE exam
• Pressure notes for SEE
• Force notes for SEE
• Important Questions of Gas and Gas Law grade XII

Thermometer:

Name of thermometric liquid:

1. Mercury (Freezing point = -39°c and boiling point= 357°c
2. Alcohol (Freezing point = -117°c and boiling point= 78°c

Thermometer: It is used to measure temperature.

Types: a)Mercury or Clinical thermometer
b) Alcohol thermometer
c) Digital thermometer
d) Maximum and minimum thermometer, etc.

Mercury or Clinical thermometer: It is used by the doctor to measure the temperature of the human body. It is a mercury thermometer. The normal body temperature is 37°c (98.6°F).

Digital thermometer: It is used by the thermistor at one end. Its reading is more accurate than Mercury thermometer.

Alcohol thermometer: The freezing point of an alcohol thermometer is -117°c and boiling point is 78°c. So, it is suitable to measure the temperature of the very cold region.

Maximum and Minimum thermometer: It uses mercury and alcohol as the thermometric liquid. It is U-shape in construction and used to measure maximum and the minimum temperature of an environment.

Heat Equation:

Definition: According to this equation the heat lost by not body is equal to the heat gained by the cold body.

• • Heat lost= Heat gained
    m₁S₁(t₁-t)= m₂s₂(t-t₂)
  • It is also called Principle of calorie try
  • Explanation: 
    Case-1
    
    mass= m₁
    Specific heat capacity= s₁
    Temperature= t₁°c
    ∴Heat lose= m₁S₁(t₁-t)
    Case-2
    
    mass= m₂
    Specific heat capacity= s₂
    Temperature= t°c
    ∴Heat gained= m₂s₂(t-t₂)
  • ∴ Heat lost= Heat gained
    or, m₁S₁(t₁-t)= m₂s₂(t-t₂)

The specific heat capacity of water is maximum: (4200J/14°). So, the water is heated slowly and cooled slowly.

Example: a) water is used in automobile engine as a heat absorber due to high specific heat capacity. It slowly absorbs heat for a long time.

b) The hot water bottle is used in a hospital to release stomach pain because of the specific heat capacity of water is more and it slowly cools down.

c)The temperature fluctuation is low on the island because it is surrounded by water which specific heat capacity is high. So, it gains or loses heat very slowly.

The specific heat capacity of sand is low, so it is quickly heated and cooled: 

Example: In the desert, the day is very hot and the night is very cold due to the low specific heat capacity of sand which is quickly heated in a day and quickly cooled in the night.

Answer these questions:

1. What is heat? On which factors does the amount of heat depend?
   Ans: The heat is a form of energy which produces a sensation of warmth (Hotness).
   The amount of heat depends on the speed of a particle.
2. Mention the effect of heat.
   Ans: The effect of heat is given below:
   a) Change in temperature.
   b) Change in physical states, etc.
3. What is the temperature? How it is measured?
   Ans: The degree of hotness or coldness of a body is called Temperature.
   It is measured by the thermometer.
4. Differentiate between heat and temperature.
   Ans: The differentiate between heat and temperature are given below:

   Heat	Temperature
   It is a form of energy which produces the sensation of warmth.	It is the degree of hotness or coldness of an object.
   Its SI unit is Joule (J).	Its SI unit is Kelvin (k).
   It is measured by a calorimeter.	It is measured by a thermometer.

5. What is a thermometer? What are the parts of thermometer?
   Ans: The thermometer is a device which is used to measure the temperature of an object.
   The parts of the thermometer are given below:
   a) Bulb
   b) Mercury
   c) Glass tube
   d) Temperature
   e) Capillary tube
   f) Constriction, etc.
6. Define:
   a) Specific heat capacity: The amount of heat required to raise the temperature of a 1kg substance by 1°C is called Specific heat capacity (S).
   b) One Calorie heat: The amount of heat used to raise the temperature of a 1gm substance by 1°C is called Calorie.
   c) Heat capacity: The amount of heat required to raise the temperature of an object through 1°c is called Heat capacity.
7. What do you mean by the fact that the specific heat capacity of water is 4200 J/kg° c?
   Ans: Specific heat capacity of water is 4200 J/kg°c because it slowly absorbs heat for a long time and releases heat after a long time.
8. Mention some effect of the highest specific heat capacity.
   Ans: Some  effect of highest specific heat capacity are given below:
   a) Aquatic life will be in hazards due to high heating and freezing point.
   b) Water will impure.
   c) Global warming, etc.
9. What is the heat equation?
   Ans: The amount of heat lost or gained by an object is equal to the product of mass, specific heat capacity and change in temperature are called the Heat Equation.

Give reasons:

1. Water is used to cool the engines of vehicles.
   Ans: Water is used to cool the engines of vehicles because it can absorb a large amount of heat from the hot engine without raising the temperature by a significant value.
2. A thick glass tumbler cracks when hot water is poured into it.
   Ans: A thick glass tumbler cracks when hot water is poured into it because when hot water is poured into the glass, it can’t absorb hot water and got cracked.
3. Honey solidifies from the bottom whereas water solidifies from the top.
   Ans: Honey solidifies from the bottom whereas water solidifies from the top because water’s density decreases and volume increases and it solidifies from the top but honey’s density decrease and its volume decrease.
4. It is very hot during the day and very cold at night.
   Ans: It is very hot during the day and very cold at night because during day sand gets heated due to sun rapidly but during night sand losses heat rapidly and gets cool faster.
5. Temperature of coastal region remains fairly constant.
   Ans: Temperature of the coastal region remains fairly constant due to the high specific heat capacity of water (4200 J/kg°c). The water plays a vital role in temperature fluctuation.

Numerical problems:

a) How much heat is required to increase the temperature of 5kg of water from 20°c to 70°c? (Given specific heat capacity of water= 4200 J/kg°c)
Given data,
m= 5kg
s= 4200 J/kg°c
t= 70°-20°c = 50°c
we know that,
H= s×m×t
= 4200×5×50
= 105×10⁴ Joule
= 1.05×10⁶ Joule

∴So, 1.05×10⁶ Joule heat is required to increase the temperature of 5kg of water from 20°c to 70°c.

b) Calculate the final temperature of a pressure cooker of mass 1.5kg and temperature 30°c, when it is heated with 7.5×10⁴ Joule. (The specific heat capacity of aluminum is 1000 J/kg°c)
Given data,
H= 7.5×10⁴ Joule
s= 1000 J/kg°c
m= 1.5kg
t= t₂-t₁
=t₂-30
we know that,
H= m×s×t
or, t= H/m×s
or, t₂-30 = 7.5×10⁴/1.5×1000 = 5×10/1
or, t₂= 5×10+30
∴t₂= 80°c∴So, the final temperature is 80°c.

c) The temperature of 20kg water in the radiator of an engine of a car is 30°c. It the temperature of the water increases to 100°c after the engine is heated. What quantity of heat is absorbed by the water?
Given data,
Mass(m)= 20kg
initial temperature (t₁)= 30°c
Final temperature (t₂)= 100°c
Change in temperature (dt)= t₂-t₁= 100°-30°= 70°c
Specific heat capacity (s)= 4200 J/kg°c
Amount of heat gained (Q)= ?
we know that,
Q= m.s.d.t
= 20×4200×70°
= 5880000
=5.88×10⁶ Joule

∴The amount of heat gained is 5.88×10⁶ Joule.

d) What will be the quantity of heat required to raise the temperature of 2kg paraffin by 10°c if 44000 Joule of heat energy is required to raise the temperature of the paraffin by 20°c?
Given data,
Mass (m)= 2kg
Specific heat capacity (s)=?
we have,
H=s.m.t
or, 44000= s×2×20
or, s= 44000/20×2
∴ s= 1100Now,
Q=m.s.t
=2×1100×10
=2.2×10⁴ Joule
∴ The quantity of heat required to raise the temperature is 2.2×10⁴ Joule

e) Hot water of 100°c is added to 300g of water at 0°c and the final temperature of the mixture reached 40°c. Find the mass of hot water added. (Given, the specific heat capacity of water= 4200° J/kg°c)
Given data,
Condition- i
t₁= 100°c
m₁=?
S₁= 4200 kg°c

Condtion- ii
t₂= 100°c
m₂=?
S₂= 4200 kg°c
∴t= 40°c
we know that,
m₁s₁(t₁-t)= m₂s₂ (t-t₂)
or, m₁= m₂s₂ (t-t₂)/s₁(t₁-t)
or, m₁= 0.3×40/60= 1.2/6= 0.2kg

∴Required amount of hot water is 0.2 kg.

f)The temperature of the water is 5°c in the winter season. If 20 liters of water is to be heated to 35°c for taking a bath. Calculate the amount of heat required for it.
Given data,
s= 4200 J/kg
Mass (m)= 20kg
temperature (t)= 30°c
we know that,
H= s.m.t
=4200×20×30
= 2.52 ×10⁶

∴The amount of heat required for it is 2.52 ×10⁶

g) For taking a bath, water at 40°c is required. Calculate the mass of water at 15°c to be added to 80kg water at 80°c for making it suitable for bathing.
Given data,
t= 40°c
t₁= 15°c
m₂= 80kg
t₂= 80°c
s= 4200 j/kg
m₁=?
we know that,
m₁s₁ (t₁-t)= m₂s₂ (t-t₂)
or, m₁= m₂s₂ (t-t₂)/s₁ (t₁-t)
or, m₁= 80×(40-80)/ 15-40
or, m₁= 80× (–40)/–20
or, m₁= 3200/ 25
or, m₁= 128kg

∴ Mass of water is 128 kg.