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1. A thermostat is a device which maintains the temperature of a place or an object constant. 

2. The word thermostat is derived from two Greek words, ‘thermo’ meaning heat and ‘static’ meaning staying the same.

3. Thermostats are used in any device or system that gets heated or cools down – to a pre – set temperature. It turns an appliance or a circuit on or off when a particular temperature is reached. 

4. Devices which use thermostat include building heater, central heater in a room, air conditioner, water heater, as well as kitchen equipment including oven and refrigerators. 

5. Sometimes, a thermostat functions both as the sensor and the controller of a thermal system.

The silvered walls reflect radiated heat back to the liquid in the flask.

C) Q = mS Δt

1. Steel is metal and it is a good conductor of heat. So due to hot milk it becomes hot and it is difficult to hold. Person’s hand get burnt due to it. 

2. So it is better to hold in a handkerchief because handkerchief is made up of cloth which is a bad conductor of heat. So your hand does not feel hot.

The halwai wrap up cloth around the end of his slotted spoon while stirring the boiling milk in his large kadhai because

(i) His slotted spoon is made up of metal and metal is a good conductor of heat so due to constant heating spoon gets very hot which makes hand to get burnt,

(ii) But cloth is a bad conductor of heat so it does not allow heat to reach till hand and halwai does not feel hot when he stirs the boiling milk.

(c) hotter to colder region

(b) condensation

BC = melting 

DE = vaporization curve.

1. The average kinetic energy of molecules/particles of the hotter body is more than the colder body. 

2. So we can say that the temperature of a body is an indicator of the average kinetic energy of molecule of that body. 

3. So the average kinetic energy of molecules is directly proportional to the absolute temperature. 

Process of evaporation is effected by surface area, wind speed, humidity, and temperature. 

Ex: 

1. The water kept in a china dish evaporates faster than in a cup because of more surface area. 

2. Water in wet the clothes are kept under fan evaporates faster than in normal conditions. 

3. Water in wet clothes evaporates faster on a less humid day than on a more humid day.

a) Joule / Kilogram-Kelvin

b) Lead, Copper, Iron, Aluminium, Water

c)  Lead

d) Q = mS∆T = 1000 × 0.115 × 10 = 1150 cal.

Correct option is  B) 200 ml

The examples to explain that evaporation is a cooling process are 

1. Drying of wet clothes. 

2. When the floor is washed with water, the water on the floor disappears. 

3. Sweating, etc.

Correct option is  B) Heat

B) from a body at higher temperature to lower temperature

C) temperature difference

Lord Kelvin (1824 – 1907): 

Lord Kelvin of Scotland studied at Cambridge University, was a champion rower, and later became a professor of natural philosophy at the University of Glasgow.

Lord Kelvin invented the Kelvin scale in 1848 used on thermometers.

The Kelvin scale measures the ultimate extremes of hot and cold.

Kelvin developed the idea of absolute temperature. It is called the second law of thermodynamics and developed the dynamical theory of heat.

In the 9th century, scientists were researching the possibility of the lowest temperature. Time Kelvin scale uses the same units of Celsius scale but it starts at absolute zero.

Absolute zero is 0°C which is – 273 K

Temperature measured on the Kelvin scale is called Absolute Temperature.

The bodies possess kinetic energy when they are in motion.

Pigs do not have sweat glands. Water in the mud evaporates and helps the pig to be cool from heat. So pigs toil in the mud during summer.

The correct option is C) iii, iv, ii, i.

Space is left between small stretches while making cemented roads in order to avoid accidents due to the expansion.

1. The capillary tube required to be very long. 

2. The increase in the water level cannot be easily visible.

The jerk to the thermometer will allow the mercury in or above the kink to flow into the bulb so that the mercury level is below normal temperature.

1. The normal temperature of human body is 37°C. 

2. The clinical thermometer is used to mea sure the temperature of human body only. 

3. The digital thermometer do not use mercury. 

4. Poor conductors are known as insulators. 

5. Heat is always transfer from hot, bodies to cooled bodies. 

6. Black or Dark coloured objects absorbs more heat.

At night the water cools down more slowly than the land. So the cool air from the land moves towards the sea. It is the land breeze.

During the day the land gets heated faster than the water. The hot air rises up and cooler air from the sea rushes towards the land. This is called the Sea breeze.

Such types of materials which help in transfer of heat from one place to another are called “medium”.

Solid, liquid and gaseous substances act as medium for transfer of heat

The materials which do not allow heat to pass through them easily are poor conductors or insulators. Eg : Wood, plastic etc.,

The materials which allow heat to pass through them easily are Conductors, eg : All metals.

The process of transfer of heat in the form of waves is called radiation. Radiation does not need any material medium. 

The transfer of heat without any media is called Radiation. When we sit in front of a room heater, we get heat by radiation. The Sun heat is also transfer through radiation because most part of the space between the earth and the Sun there is no media or air.

Take a round bottom flask. Fill it with \(\frac{2}{3}\) part of water. The other equipments should arrange as in the figure. Heat the water by placing the candle just below the flask. Observe when water is heated near the flame gets hot and rises up. The cold water from the sides moves down towards the source of heat. This process continues till the whose water gets heated. This mode of heat transmission is known as Convection.

The process by which heat is passed from the hotter end to colder end in solids. This is known as Conduction. All metals are good conductors of Heat.

(c) copper is a better conductor of heat than the stainless steel

Thermal expansion of bimetallic strips used as a heat operated switch in the circuit of automatic equipment’s like iron box, fire alarms, electric heater etc. Some thermometers work on the principle of expansion of liquids In automobile engines useful work is done by the expansion of gases.

Wash the thermometer with an antiseptic solution. Hold it firmly, give it a few jerks. The Jerks will bring the level of mercury down. Ensure that it falls below 35°C. Now place the thermometer under the tongue of the person. After one minute take the thermometer out and note the reading. This is the temperature of that person. The temperature should always be stated with its unit °C

Bimetallic strip thermometers include two different metals that are bonded together and expand at different rates as they warm up often, long bimetallic, strips are wound into a coil and used with a dial they have different rate of exampsion.

In a clinical thermometer kink plays an important role. Kink prevents the mercury present in the capillary to fall back in the bulb. So it seprates the mercury at high temperature and cool mercury and allows the user to note the reading when the thermometer is taken out.

a) What type of climate changes do you observe in last ten years? 

b) What changes have been made in the cultivation of crops due to climate changes?

1. Wash the thermometer with water or an antiseptic solution before and after use. 

2. Before use, the level of mercury should be less than 35°C, otherwise shake it. 

3. Don’t touch the bulb while taking reading.

4. Handle the thermometer carefully, because it is a glass ware. 

5. Take the reading after increasing of the mercury level is stopped.

1. Thermometer should be washed before and after use, preferably with an antiseptic solution. 

2. Ensure that before use the mercury level is below 35°C. 

3. Read the thermometer keeping the level of mercury along the line of sight. (Refer fig 4.3 in the text p.no. 37) 

4. Handle the thermometer with care. If it hits against some hard object, it can break. 

5. Don’t hold the thermometer by the bulb while reading it.

The capillary has a narrow bend called constriction. The range of clinical thermometer is between 35° C and 42° C.

1. Precautions to be taken while using a clinical thermometer. 

2. Thermometer should be washed before and after each use, preferably with an antiseptic solution. 

3. Do not wash the thermometer with hot water. 

4. Ensure that before use the mercury level is below 35° C. 

5. Read the thermometer keeping the level of mercury along the line of sight. 

6. Handle the thermometer with care, as you handle any glass articles. 

7. Don’t hold the thermometer by the bulb while reading it.