Magnetic Field and Field Lines - UNSOLVED PRACTICE SET

Q7. Define a magnetic field. How can the direction of a magnetic field at a point be determined using a compass needle?

Q8. Describe how you would use iron filings to map the magnetic field pattern of a bar magnet. What pattern would you observe?

Q9. State three important properties of magnetic field lines.

Q10. Why do magnetic field lines never cross each other? What would it mean physically if two field lines did cross at a point?

Q11. Inside a bar magnet, in which direction do the magnetic field lines run — from N to S or S to N? How does this make the field lines form closed loops?

Q12. A compass placed near a bar magnet aligns itself along the field lines. Explain what happens to the compass needle as you move it from near the north pole to near the south pole of the magnet.

Q13. Describe an experiment to plot the magnetic field lines around a bar magnet using a compass. Your answer must cover:
(a) the apparatus needed,
(b) the step-by-step procedure for plotting field lines using a compass,
(c) the resulting pattern of field lines (description),
(d) the three key properties of magnetic field lines demonstrated by this pattern, and
(e) how the same experiment could be done with iron filings instead, and what advantage/disadvantage this method has compared to the compass method.

Q14. Explain the concept of magnetic field strength and how it varies in space around a bar magnet. Your answer must cover:
(a) what determines the strength of a magnetic field at a point,
(b) why field lines are closer together near the poles,
(c) how the field lines indicate both the direction and relative strength of the field,
(d) describe the magnetic field pattern between two bar magnets placed with like poles facing each other, and
(e) describe the pattern when unlike poles face each other (a uniform field region)

Q15. A student in a school laboratory in Bhopal is given a bar magnet, a sheet of paper, iron filings, and a small compass.
(a) Describe the complete experimental setup to visualise the magnetic field pattern.
(b) What precautions should the student take while sprinkling iron filings?
(c) How would the field pattern change if the bar magnet were replaced with a horseshoe magnet?
(d) The student notices the field lines near the centre of the magnet (on the side) appear less dense — what does this tell us?
(e) How does the Earth itself act like a giant bar magnet, and how does this relate to how a compass works?

Q16. Two bar magnets are placed on a table with their north poles facing each other, 5 cm apart.
(a) Sketch (or describe in detail) the resulting magnetic field pattern between and around the magnets.
(b) Where would the magnetic field be zero (a 'neutral point')?
(c) If a small compass is placed exactly at this neutral point, what would happen to its needle?
(d) How would the pattern change if one magnet were flipped so that a north and a south pole face each other?

Q17. A student plots field lines around a bar magnet and observes that the lines are much closer together near the poles than near the middle of the magnet (along its side).
(a) What does this observation tell us about the relative field strength at these locations?
(b) If the student were to place a small compass at three positions — near a pole, at the side midpoint, and far away from the magnet — describe how the compass needle's behaviour (deflection and alignment) would differ at each position.
(c) Estimate (qualitatively) how the field strength changes as distance from the magnet increases.

Q18. In an Indian science exhibition, a student demonstrates magnetic field lines using iron filings sprinkled on a glass sheet placed over a bar magnet.
(a) Explain why the iron filings arrange themselves into curved lines rather than staying randomly scattered.
(b) If a second identical bar magnet is placed below the glass sheet, parallel to the first but with opposite polarity facing up, predict and describe the new pattern of iron filings.
(c) Why is this demonstration considered 'indirect' evidence of a magnetic field rather than 'direct' visual evidence?