CBSE Class 7 Science Changes And Reactions And Electricity Worksheet

I. Choose the correct answer:

1) An acid reacts with a base to form a salt & water. This type of reaction is called

a) Combination reaction b) Neutralization reaction

c) Displacement reaction d) Decomposition reaction

2) Filament is made up of

a) Tungsten b) Aluminium c) Copper d) Tin

3) Resistance depends on

a) Material b) Thickness c) Length d) All of these

4) A length of wire wound closely together is called a

a) Resistance b) Coil c) Soft iron d) Fuse

5) The thin & coiled wire inside a bulb is called:

a) Terminal b) filament c) connecting wire d) supporting wire

6) Curdling of milk is a

a) Chemical change b) Physical change c) Both (a) & (b) d) None of these

7) Rusting takes place in

a) Air-free moisture b) Moisture-free air c) Moist air d) None of these

8) The digestion of food is a

a) Physical change b) Chemical change c) Both (a) & (b) d) None of these

II. Fill in the blanks.

1) An electric cell has _________ terminals.

2) A group of connected cells is called a __________

3) A thin wire has a __________ resistance than a thick wire.

4) The lower the resistance, the _________ is the current.

5) The iron used in nails is called _______ iron.

6) Melting of wax is a _______ change.

7) Cooking of food is a _______ change.

8) In a ___________ reaction, two or more reactants add up to form a product.

9) The forming of rust is called _______.

10) Hydrocarbons are compounds made of _____ and _______.

III. State true or false.

1) Electric current flows through a closed circuit.

2) A long wire has a higher resistance than a short wire.

3) The higher the resistance, the lesser is the heat produced.

4) The greater the voltage across a device, the greater is the current through it.

5) Overload & short circuit cause minimum heating.

6) When a substance is burnt only light is emitted.

7) Magnesium combines with oxygen of air to form magnesium oxide.

8) New substances are formed in a physical change.

9) The mixture of water and alcohol forms a heterogeneous mixture.

10) Petrol, diesel and LPG contain mixtures of hydrocarbons.

IV. Match the following.

               A                                                         B

1) Electromagnets                                  a) baking soda

2) Nichrome                                            b) steel

3) sodium hydrogencarbonate                c) heating element

4) metallic solids                                      d) red-brown solid

5) rust                                                       e) washing machines

V. Define.

1) Physical change 2) Chemical change 3) Melting 4) Freezing

5) Vaporisation 6) Condensation 7) Rusting 8) Combination reaction

9) Decomposition reaction 10) Displacement reaction 11) Neutralization reaction 12) Current

13) Electric circuit 14) Circuit diagram 15) Resistance 16) Fuse

17) Coil 18) electromagnet

VI. Give reasons

1) Freshly cut apple or brinjal turns brown.

2) Burning of magnesium ribbon is considered a chemical change