# NCERT Class 7 Science Model Paper 2 Questions and Answers Part 2 (For CBSE, ICSE, IAS, NET, NRA 2022)

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

Ans: (ii) Describe an experiment to show that electric current produces a magnetic effect.

(i) No! Electromagnets can only attract magnetic materials. Plastic bag is a non-magnetic material and will not be attracted by an electromagnet. Hence, an electromagnet cannot be used for separating plastic bags from a garbage heap.

(ii) In 1820, Hans Christian Oersted, a physics professor performed an experiment to show that a magnetic field is set up around a current carrying conductor. The experiment was performed as follows:

(a) Electric current was allowed to pass through a metallic wire AB, placed parallel to the axis of a magnetic compass kept directly below the wire. The needle of the magnetic compass was found to deflect from its normal position as shown in fig.

(b) Electric current was again allowed to pass through the same wire AB but now in opposite Direction. It was found that the needle of the magnetic compass again deflected from its normal position but in opposite direction as shown in fig. 26.

11. (i) Draw the image formation by convex lens when object is placed (a) between optical center and focus (b) at infinity

(ii) Write any two uses of plane, concave and convex mirror each.

OR

(i) Name the type of mirror which can be used to see enlarged image of an object. Also draw a ray diagram of this type of mirror which from virtual and magnified image.

(ii) What is Newton՚s colour disc? What does the Newton՚s colour disc experiment establish about the nature of white light?

Ans: (i)

(ii) Plane mirror: Periscope, Kaleidoscope

Concave mirror: Shaving mirror, In solar cooker

Convex mirror: Street lamps, Rear view mirrors.

OR

(i) Concave mirror

(ii) Newton՚s colour disc is a metallic or cardboard disc painted with seven Colours of the spectrum (see fig. 46) . The sector of each colour is painted in the order and ratio of amount of colour found in solar spectrum, i.e.. , VIBGYOR. When the disc connected to a wheel is rotated at a high speed in a vertical plane, disc appears dull white. It establishes that recombination of the spectrum Colours (VIBGYOR) gives white light.

The colored disc appears white because of a property of our eyes called persistence of vision.

This means that an image formed by the eye remains for a fraction of a second. When the disc is rotated at a high speed, the images of the different Colours overlap in our eyes and the brain perceives it as white.

## Section – B: Chemistry

12. The pH of pure water is

(1) 0.0

(2) 1.0

(3) 7.0

(4) 11.0

Ans: Option (3)

13. The type of reaction is

(1) Synthesis

(2) Single displacement

(3) Decomposition

(4) Combination

Ans: Option (2)

14. The water table in an area will go down when

(1) We do not use ground water.

(2) We use ground water faster than it is replenished.

(3) We use ground water slowly than it is replenished.

(4) We plant too many trees causing loss of water by transpiration.

Ans: Option (2)

15. Which disease is not produced by contaminated water?

(1) Dysentery

(3) Typhoid

(4) Cholera

Ans: Option (2)

16. Assertion: Salt converts into base only on dissolution in water.

Reason: When salt is mixed with ice, it lowers the freezing point of ice considerably.

(1) Assertion is true, reason is false.

(2) Assertion is false, reason is true.

(3) Both assertion and reason are true.

(4) Both assertion and reason are false.

Ans: Option (2)

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