Class 7 Science - Chapter Electric Current and Its Effects NCERT Solutions | Draw the circuit diagram to represent th

Draw in your notebook the symbols to represent the following components of electrical circuits: connecting wires, switch in the ‘OFF’ position, bulb, cell, switch in the ‘ON’ position, and battery

Fig.14.22 shows four cells fixed on a board. Draw lines to indicate how you will connect their terminals with wires to make a battery of four cells.

Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.

In the circuit shown in Fig. 14.25

(i) Would any of the bulb glow when the switch is in the ‘OFF’ position?
(ii) What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position?

Will the compass needle show deflection when the switch in the circuit shown by Fig.14.24 is closed?

When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.

An electrician is carrying out some repairs in your house. He wants to replace a fuse by a piece of wire. Would you agree? Give reasons for your response.

Zubeda made an electric circuit using a cell holder shown in Fig. 14.4, a switch and a bulb. When she put the switch in the ‘ON’ position, the bulb did not glow. Help Zubeda in identifying the possible defects in the circuit.

Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (T/F)
(b) When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T/F)
(c) An electromagnet does not attract a piece of iron. (T/F)
(d) An electric bell has an electromagnet. (T/F)

Fill in the blanks:

(a) Longer line in the symbol for a cell represents its terminal                       .
(b) The combination of two or more cells is called a                     .
(c) When current is switched ‘on’ in a room heater, it                            .
(d) The safety device based on the heating effect of electric current is called a                             .

State similarities and differences between the laboratory thermometer and the clinical thermometer.

State differences between acids and bases.

Classify the changes involved in the following processes as physical or chemical changes:
(a) Photosynthesis
(b) Dissolving sugar in water
(c) Burning of coal
(d) Melting of wax
(e) Beating aluminium to make aluminium foil
(f ) Digestion of food

Name the elements that determine the weather of a place.

Fill the missing word in the blank spaces in the following statements:

(a) Wind is——————air.
(b) Winds are generated due to —————— heating on the earth.
(c) Near the earth’s surface __________air rises up whereas ___________ air comes down.
(d) Air moves from a region of ——— pressure to a region of ———.

In addition to the rock particles, the soil contains

(i) air and water
(ii) water and plants
(iii) minerals, organic matter, air and water
(iv) water, air and plants

Why does an athlete breathe faster and deeper than usual after finishing the race?

Match structures given in Column I with functions given in Column II.

Column I                           Column II
(i) Stomata                        (a) Absorption of water
(ii) Xylem                           (b) Transpiration
(iii) Root hairs                    (c) Transport of food
(iv) Phloem                        (d) Transport of water
                                          (e) Synthesis of carbohydrates

Fill in the blanks:

(a) Production of new individuals from the vegetative part of parent is called_____________.
(b) A flower may have either male or female reproductive parts. Such a flower is called_____________.
(c) The transfer of pollen grains from the anther to the stigma of the same or of another flower of the same kind is known as _____________.
(d) The fusion of male and female gametes is termed as _____________.
(e) Seed dispersal takes place by means of _____________, _____________ and _____________.

Classify the following as motion along a straight line, circular or oscillatory motion:

(i) Motion of your hands while running.
(ii) Motion of a horse pulling a cart on a straight road.
(iii) Motion of a child in a merry-go-round.
(iv) Motion of a child on a see-saw.
(v) Motion of the hammer of an electric bell.
(vi) Motion of a train on a straight bridge.

In places of hot climate it is advised that the outer walls of houses be painted white. Explain.

How is clayey soil useful for crops?

Why is it necessary to excrete waste products?

Explain why there is a need of variety of animals and plants in a forest.

Which of the statements given below is correct?

(i) In winter the winds flow from the land to the ocean.
(ii) In summer the winds flow from the land towards the ocean.
(iii) A cyclone is formed by a very high-pressure system with very high-speed winds revolving around it.
(iv) The coastline of India is not vulnerable to cyclones.

Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.

Indicate the type of climate of the following areas:

(a) Jammu and Kashmir: _________________________________
(b) Kerala: ____________________________________________
(c) Rajasthan: __________________________________________
(d) North-east India: _____________________________________

Match the items given in Column I with one or more items of Column II.

Column I                                          Column II
(a) A plane mirror                              (i) Used as a magnifying glass.
(b) A convex mirror                           (ii) Can form image of objects spread over a large area.
(c) A convex lens                              (iii) Used by dentists to see enlarged image of teeth.
(d) A concave mirror                         (iv) The image is always inverted and magnified.                                                                                                                    (e) A concave lens                            (v) The image is erect and of the same size as the object.
                                                         (vi) The image is erect and smaller in size than the object.

Take three test-tubes. Fill æth of each with water. Label them A, B and C. Keep a snail in test-tube A, a water plant in test-tube B and in C, keep snail and plant both. Which test-tube would have the highest concentration of CO₂?

Micro-organisms act upon the dead plants to produce
(i) sand     (ii) mushrooms     (iii) humus     (iv) wood