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PHYSICS FORM 4MRSM KUALA KLAWANG
HEAT
What do you observe?
What is Heat?
When you touch the hot pot what do you feel?
High temperature
High heat
Relationship between Temperature and Heat
Heat is a form of energy being transferred from a hot body to a cold body.
The total amount of heat in a body depends on the mass, material and temperature of the body.
Relationship between Temperature and Heat
Temperature is a measure of the degree of hotness of a body.
A hot body has a high temperature whereas a cold body has a low temperature.
Relationship between Temperature and Heat
TEMPERATURE HEAT
The degree of hotness of a body
A form of energy
Base quantity Derived quantity
Unit: kelvin (K) or degree celcius (oC)
Unit : joule (J)
Can be measured using the thermometer.
No specific measuring equipment.
4.1: UNDERSTANDING THERMAL EQUILIBRIUMThermal equilibriumLiquid in glass thermometer
4.2: UNDERSTANDING SPECIFIC HEAT CAPACITYSpecific heat capacityApplications
4.3: UNDERSTANDING SPECIFIC LATENT HEAT4.4: UNDERSTANDING THE GAS LAWS
Boyle’sCharles’Pressure
HEAT
Discussion
Which has a higher temperature ?: A steaming cup of tea or a huge iceberg?
The answer is obvious -- the tea is at a higher temperature.
But which of the two has more heat?
.The total amount of heat in a body depends on the mass, material
and temperature of
the body
4.1: THERMAL EQUILIBRIUM
4.1.1: THERMAL EQUILIBRIUM
Energy is transferred at a faster rate from the hotter object # 1 to the cooler object #2.
Energy is transferred at a slower rate from the cooler object # 2 to the hotter object # 1.
The hot object loses energy while the cold object gains energy.
Thermal equilibriumThis causes the hot object to cool down while the cold object warms up.
The two objects in thermal equilibrium have the same temperature
After some time, the rates of energy transfer between the two objects become equal.
Energy Transfer
After some time, the rates of energy transfer between the two objects become equal.
There is no net heat transfer between the two objects. The two objects are said to be in Thermal equilibrium.
energy
Applications of thermal equilibriumWhen raw food, e.g. meat is put in the oven, heat from the oven is transferred to it.This process will continue until thermal equilibrium is reached between the food and the oven.
The temperature of the food and the oven will be the same when the food is cooked.
Electric oven /
microwave oven
Applications of thermal equilibrium
refrigerator
When food are kept in the refrigerator, the heat from the food is released to the cold air in the fridge.
This process continues until thermal equilibrium is reached between the food and the fridge.
The temperature of the food will be equal to the temperature of the fridge.
Hence the food are maintained in good condition
Applications of thermal equilibrium
Taking the temperature of a sick person
The thermometer is placed below the tongue, so that the thermometer is in contact with the mouth and tongue of the patient.
After about a minute, thermal equilibrium is reached between the thermometer and the patient’s tongue/body.
Heat will flow from the patient’s tongue to the bulb of the thermometer
Therefore, the temperature reading shows the body temperature of the patient.
4.1.2: THERMOMETER
Heat will flow from the tongue to the bulb ,and this process will continue until TE is reached.
The thermometer reading shows the body temperature.
4.2: HEAT CAPACITY
27oC 100oC
Same volume of water at different temperatures.
The water which is at higher temperature has a greater quantity of heat compared with the water which is at a lower temperature.
HOT WATER
glass
jug
Hot water in both the glass and the jug.
The water in the jug is hotter to touch compared to the water in the glass.
The water in the jug has a greater quantity of heat compared to the water in the glass, because the water in the jug has a greater mass.
Iron plate Mica plate
An iron plate and a mica plate of the same mass are put into the oven.
After half a minute , the iron plate has a greater increase in temperature compared to the mica plate.
This shows that heat absorbed is dependent on the type of materials.
2 factors affecting heat capacities…i) ________________________ii) ________________________
Specific Heat capacity: the amount of heat required to increase the temperature of 1 kg of a substance by 10C.
Definition
SPECIFIC HEAT CAPACITY
Amount of heat , q (joule)MASS, m (KILOGRAM)CHANGE IN TEMPERATURE, Дθ (0C )SPECIFIC HEAT CAPACITY, c
c = Q___ m Δθ
Unit : J kg-1 0C-1
Applications of heat capacity
sparkler
The sparks of a sparkler do not burn the hand of a person.
However if the person touches the glowing part of the sparkler, he/she will get burn.
This because the sparks have a smaller amount of heat compared to the glowing sparkler
Applications of heat capacity
A bowl of vegetable soup
A bowl of vegetable soup is too hot to drink.
However, the vegetable in the soup can be eaten slowly although the soup and the vegetables are of the same temperature.
Why?
