Exploring Magnets — Hard

Q1. Consider the following statements about magnets of different shapes: I. A spherical magnet has its poles at two opposite points on its surface. II. A disc magnet has two poles, one on each flat face. III. A magnet of any shape can be made with a single isolated pole if the shape is suitable. Which of these statements are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three are correct

Q2. Consider the following statements about today's magnets: I. Modern magnets are made only from naturally occurring lodestone. II. Magnets can be made from pieces of iron and other materials. III. Magnets found in pencil boxes, stickers and toys are artificial magnets. Which are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three are correct

Q3. Assertion (A): A copper coin is not attracted by a magnet. Reason (R): All metals are magnetic materials. Choose the correct option.

• A. Both A and R are true, and R is the correct explanation of A.
• B. Both A and R are true, but R is NOT the correct explanation of A.
• C. A is true, R is false.
• D. A is false, R is true.

Q4. A student brings a magnet near a steel paper-clip and a brass key. She observes that the steel clip is attracted while the brass key is not. The best reason is

• A. Steel always contains gold, which is magnetic.
• B. Brass keys are coated with plastic, which blocks the magnet.
• C. The paper-clip has been heated, so it has become magnetic.
• D. Steel is an iron-based alloy and is magnetic; brass is mainly copper and zinc and is non-magnetic.

Q5. Assertion (A): If a bar magnet is broken into two pieces, each piece becomes a complete magnet with its own North and South pole. Reason (R): Magnetic poles always exist in pairs and cannot be isolated. Choose the correct option.

• A. Both A and R are true, and R is the correct explanation of A.
• B. Both A and R are true, but R is NOT the correct explanation of A.
• C. A is true, R is false.
• D. A is false, R is true.

Q6. On commercially sold bar magnets, the North pole may be indicated in several ways. Which of these conventions is NOT mentioned in the chapter?

• A. The letter N is printed on the pole
• B. The North pole carries a small white dot
• C. The North pole is painted red, the South pole blue
• D. The North pole is wrapped in a copper coil

Q7. An iron bar that is NOT a magnet is suspended by a thread in place of a bar magnet. Which observation is most likely?

• A. It rests strictly along the north–south direction every time.
• B. It rests along any direction; it does not always point north–south.
• C. It rotates continuously and never stops.
• D. It rests strictly along the east–west direction.

Q8. Reshma is given three identical-looking iron bars. Two are magnets and one is a plain iron bar. WITHOUT using any other material, which test will identify the plain bar most reliably?

• A. Place the bars in water — only the magnet sinks.
• B. Weigh the bars — the magnet weighs less.
• C. Smell the bars — only the magnet has a smell.
• D. Bring the bars two at a time end-to-end; the pair that always attracts (never repels) contains the plain iron bar.

Q9. Assertion (A): The North pole of a compass needle points towards geographic North. Reason (R): The geographic North of the Earth is actually a magnetic South pole. Choose the correct option.

• A. Both A and R are true, and R is the correct explanation of A.
• B. Both A and R are true, but R is NOT the correct explanation of A.
• C. A is true, R is false.
• D. A is false, R is true.

Q10. After magnetising a sewing needle, why is it placed through a cork floating in a bowl of water?

• A. To let the needle rotate freely with very little friction, so its poles can settle along north–south.
• B. To cool the needle quickly so it stays magnetic.
• C. To rust-proof the needle while it is magnetised.
• D. To increase the strength of the magnetism.

Q11. In Activity 4.4, how many times should the magnet be stroked along the needle for the needle to become a magnet?

• A. Once is enough
• B. 5–10 times
• C. 30–40 times
• D. More than 200 times

Q12. Consider these statements about distinguishing a magnet from a plain iron bar by interaction alone: I. An iron bar is always attracted by both poles of a magnet. II. Two magnets can repel each other; a magnet and an iron bar never repel. III. Repulsion (not attraction) is the only sure test of whether an object is a magnet. Which are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three are correct

Q13. Aman observes that a particular metal bar X is attracted by both the North pole and the South pole of a bar magnet, while another bar Y is attracted by only one pole of the magnet and repelled by the other. What can he conclude?

• A. Both X and Y are magnets.
• B. Both X and Y are plain iron bars.
• C. X is a plain iron bar; Y is a magnet.
• D. X is a magnet; Y is a plain iron bar.

Q14. Assertion (A): A magnet can pull a steel pin lying inside a closed glass tumbler from outside. Reason (R): The magnetic effect can act through non-magnetic materials. Choose the correct option.

• A. Both A and R are true, and R is the correct explanation of A.
• B. Both A and R are true, but R is NOT the correct explanation of A.
• C. A is true, R is false.
• D. A is false, R is true.

Q15. Looking at Table 4.2 (where wood, cardboard, plastic and glass were each placed between a magnet and a compass needle), which conclusion is most accurate?

• A. The magnetic effect is blocked by all non-magnetic sheets.
• B. The magnetic effect is blocked only by glass.
• C. There is no appreciable change in needle deflection — the magnetic effect passes through these non-magnetic materials.
• D. The magnetic effect doubles when any non-magnetic sheet is placed between.