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GSEB Solutions for Class 8 Science and Technology – Solar Equipments

GSEB Solutions for Class 8 Science and Technology – Solar Equipments (English Medium)

GSEB SolutionsMathsScience
Exercise 72:

Solution 1(a):

The water in the saucer kept in the sunlight will be hotter.

Solution 1(b):

The water in the saucer kept in the sunlight absorbs energy from the Sun and hence becomes hot.

Exercise 79:

Solution 1(a):

Parabolic solar cookers are used for baking (e.g. chapattis) and for frying because they require stronger heating.

Solution 1(b):

The limitations of a parabolic solar cooker are as follows:

  1. It cannot be used for cooking food during the night as sunshine is not available.
  2. It cannot be used in all locations as it is not always sunny in some parts of the world and in some parts the Sun is rarely out.
  3. It cannot be used if the day-sky is covered with clouds.
  4. If the appliance is not handled properly, there is a risk of accidental injury or burns.
  5. If the concentrated beams of sunlight are reflected back into the eyes from the cooker, it can damage our eyesight.

Solution 1:

GSEB Solutions for Class 8 Science and Technology - Solar Equipments-Ex-79-1

  1. Take a shallow card board box. Place a thick cardboard in the centre of the box such that it divides the box into two parts.
  2. Make few holes on the cardboard fixed vertically in the box.
  3. Paint the inner surface of the box black.
  4. Fix a mirror to the box using tape such that sunlight incident on the mirror gets reflected in the box. The heat catcher is ready.
  5. Arrange the box on a table or stand and lean the solar box against it at the most effective angle to catch the Sun’s rays. Place the food in the drying box and cover it with a sheet or cloth. This is how a solar dryer can be made.

Solution 2:

The following are the benefits of solar equipments:

  1. Solar equipments harness the energy of the Sun, which is a renewable source of energy.
  2. Apart from the initial installation investment, solar energy required by the solar equipments is free of cost.
  3. Solar equipments can be used in rural areas where installation of electricity power grids is very expensive.
  4. Solar equipments do not cause any pollution and have a positive effect on the environment.

Solution 3:

A parabolic solar cooker is used for the following purposes:

  1. It is used for cooking food like pulses, dal and vegetables.
  2. It used for roasting and baking. For example making of chapattis.
  3. It is used for frying.

Solution 4:

The following are the solar instruments used in villages:

  1. Parabolic solar cooker
  2. Solar cooker
  3. Solar dryer
  4. Solar water heater
  5. Solar cell

Solution 5:

After 45 minutes when water in both the saucers is touched, we find that the black coloured water kept in one saucer is warmer as compared to the water in the other saucer. This is because black colour absorbs more heat from the sunlight and becomes warmer.