7th Class Science Heat Temperature and Measuring Device

Temperature and Measuring Device

Category : 7th Class

Temperature and Measuring Device

The degree of hotness and coolness of an object is called its temperature. Temperature of an object can be measured with devices. Earlier thermo scope was used for measuring temperature. Now an improved instrument, "Thermometer" is used for the measurement of temperature.

Mercury inside the thermometer receives temperature and expands or contracts according to variation in the temperature. However, mercury based thermometer cannot be used for the measurement of temperature below 39°C. In that case, alcohol based thermometer is used .which freezes at - 117°C.

Reading, shown by the clinical thermometer is in the form of degree Celsius and written as °C. Water converts into vapor at' 100°C. The temperature at which water converts into vapor is called upper fixed point. Water converts into ice at 0°C and this is called lower fixed point. Rate of vaporization of water will increase with an increase in temperature.

Another scale for the measurement of the temperature is Fahrenheit and it is denoted by "F and read as degree Fahrenheit.

In this scale, the freezing point of water is defined at 32°, while the boiling point of water is defined to be 212°.

There are 100 small divisions between the lower fixed point and upper fixed point in a Celsius scale. In the Fahrenheit scale, 180 small divisions are marked.

Therefore the ratio of both the scale, °C : °F is 100 : 180 =5:9.

Another scale for the measurement of temperature is kelvin scale (also called absolute scale). In the kelvin scale water freezes at 273.16k and water boils at 373.16k.

Therefore the ratio of the interval in the kelvin scale is same as the interval in the celsius scale. The temperature of 0°K is called absolute zero temperature.

Water is converted into vapour at a certain temperature. The temperature at which water converts into vapor is called?

(a) Lower fixed point

(b) Upper fixed point

(d) All of these

(e) None of these

Answer: (b)

0°C is equal to:

(a) 243°K

(b) 234°K

(d) All of these

(e) None of these

Answer: (c)

Thermometers

Two types of thermometers are there in use. These are, laboratory thermometer and clinical thermometer. The temperature between, - 10°C to 110°C is measured by laboratory thermometer. Clinical thermometer is used for the measurement of body temperature. The body temperature varies slightly.

Therefore the range of clinical thermometer is between 35°C to 42°C. Clinical thermometer has graduated scale, on which scale is mentioned in degree Celsius and in Fahrenheit. Small division on the body of the clinical thermometer represents the temperate of degree C. The range in terms of Fahrenheit on the body of the thermometer is between 94°C to 108°C. Human body temperature on the Fahrenheit scale is 98.4°F and in the Celsius scale it is 37°C. Clinical thermometer is made up of glass tube and a liquid (mercury or alcohol or hydrocarbon based fluid) is filled inside it. As the temperature increases, volume of the mercury expands. Division on the body of the thermometer shows the increase in temperature.

Look at the following pictures of clinical thermometer

Analog thermometer Digital thermometer

Digital thermometers are widely used because of its accuracy. A digital display on it shows temperature. It requires battery for function, which is based on thermocouple. Thermocouple of the digital thermometer senses heat. And the amount of heat sensed by thermocouple is converted into electrical signal, display chart indicates heat of the body under measure.

Laboratory thermometer is generally available in the range of-10°C to 110°C. The graduated laboratory thermometer is used in the laboratory for the measurement of the temperature of chemicals and for other purposes. One small division on it shows the temperature of 1°C. It is made up of glass tube having mercury inside it. Mercury of thermometer expands when heat is sensed by the mercury bulb of the thermometer.

See the Following Picture of Laboratory Thermometer