This PSEB 7th Class Science Notes Chapter 4 Heat will help you in revision during exams.
PSEB 7th Class Science Notes Chapter 4 Heat
→ The method of determining whether an object is hot or cold by touching it is not reliable.
→ Temperature is the degree of hotness or coldness of an object.
→ The hot or cold state of an object, i.e. the temperature is measured with an instrument called a thermometer.
→ The temperature of a human or living organism is measured with a medical thermometer (or clinical thermometer)
→ A scale is present on a medical thermometer. This scale is either in Celsius [°C] or Fahrenheit [°F] or both.
→ Medical thermometers have a narrow, homogeneous tube of glass with a bulb at the bottom.
→ There is a kink near the bulb of a medical thermometer that prevents the mercury level from falling as a result of its weight.
→ Should clean with antiseptic solution before and after use of a medical thermometer.
→ The scale range of medical thermometers is from 35°C to 42°C.
→ Before using a medical thermometer, make sure that the mercury level is below 35° C.
→ If not, hold the thermometer firmly and shake it to bring a level of mercury below 35°C.
→ The normal temperature of a healthy person is 37°C or 98.4°F.
→ There are other thermometers to measure the temperature of objects.
→ One of these is the Lab thermometer. The lab thermometer ranges from -10°C to 110° C.
→ The temperature of the object should be measured with a lab thermometer when the mercury level in the thermometer becomes stable.
→ The method by which heat is transferred from the hotter end of an object to the cold end by the particles of material of the object is called conduction. Solids are heated by the conduction method.
→ Materials that transmit heat are called conductors.
→ Items made of iron, silver, copper, aluminium are heat conductors.
→ Substances that do not conduct heat well are called insulators or non-conductors, e.g. Wood, plastic, and rubber.
→ Air is not a good conductor of heat.
→ The method of heat transfer in which heat is transmitted by the motion of hot molecules of a substance is called convection.
→ Heat is transmitted in liquids and gases by the convection method,
→ In coastal areas, the wind that blows from the sea to the coast during the day is called Sea breeze.
→ In coastal areas, the air that blows from the coast to the sea at night is called land breeze.
→ Radiation is the method of transfer of heat due to the emission of radiations by hot objects without a medium.
→ Dark coloured fabrics absorb heat more than light coloured fabrics.
→ So in winter, we wear dark colours and in summer we wear light coloured clothes.
→ Woolen garments keep us warm in winter because of the air trapped in the wool fibres which is a bad conductor of heat.
→ Heat: It is an agent which produces in us the sensation of warmth. This is a kind of energy.
→ Temperature: Degree of hotness or coldness measured on a definite scale.
→ Thermometer: An instrument used to measure the temperature of an object.
→ Celsius Scale: The Celsius scale is a scale for measuring temperature. Sometimes it is also called as the centigrade scale.
→ Resistor: A substance through which heat cannot be transmitted properly is considered to be resistor or resistant to heat.
→ Conduction: This is the method of heat transfer in which heat passes from the hot end of the object to the cold end through the molecules of the material, but the molecules of the object remain fixed in their place.
→ Convection(Liquid or Gas): This is the method of heat transfer in which heat is transferred from the source of heat to the cold part due to the motion of hot molecules and the cold molecules come down to take their place. This method is used for heating liquids and gases.
→ Radiation: This is the method of heat transfer in which heat is transmitted from a hot source or body directly to a cool body without affecting the medium.
→ Sea breeze: Due to the heat of the sun during the day, the soil of the land gets heated very quickly when water molecules of the ocean are not so hot. Therefore, the air near the ground gets warmer and rises up due to being lighter.
→ To replace it, cool air begins to flow from the ocean, causing air currents to flow. The wind that blows from the ocean to the land is called the sea breeze.
→ Land breeze: Due to high heat absorption capacity, water cools later than land, due to which cold air starts flowing towards seawater which is called land breeze.
→ Fahrenheit Scale: The Fahrenheit scale is a scale designed to measure temperature.