Class 9 Magnetism Mock Test (ICSE)

Topics in Magnetism

• Induced magnetism
• Magnetic field lines
• Earth's magnetic field and neutral points
• Electromagnets and their uses

Magnetism practice questions with answers

1. Q1Multiple choice·1 mark
   At a neutral point formed in the magnetic field of a bar magnet:

   1. (a)the magnetic field of the magnet is equal and opposite to the vertical component of Earth's magnetic field.
   2. (b)the magnetic field of the magnet is equal and opposite to the total magnetic field of the Earth, including its vertical part.
   3. (c)the magnetic field of the magnet is equal and opposite to the horizontal component of Earth's magnetic field.
   4. (d)the magnetic field of the magnet is perpendicular to the horizontal component of Earth's magnetic field.
   Show answer and step marks

   1. Correct option: (c) the magnetic field of the magnet is equal and opposite to the horizontal component of Earth's magnetic field. At a neutral point the two horizontal fields cancel, so a compass needle there shows no fixed direction; the vertical component of Earth's field is not cancelled.+1

   Answer: (c)
2. Q2Multiple choice·1 mark
   When an unmagnetized soft iron bar is placed near the north pole of a bar magnet, the end of the soft iron bar closer to the magnet acquires:

   1. (a)no magnetic polarity
   2. (b)a south polarity by induced magnetism
   3. (c)permanent magnetic properties
   4. (d)a north polarity by induced magnetism
   Show answer and step marks

   1. Correct option: (b) a south polarity by induced magnetism+1

   Answer: (b)
3. Q3Multiple choice·1 mark
   To increase the strength of the magnetic field of an electromagnet, which of the following changes should be made?

   1. (a)Decrease the number of turns in the coil
   2. (b)Increase the current flowing through the coil
   3. (c)Decrease the magnitude of current
   4. (d)Use a soft iron core and replace it with a steel core
   Show answer and step marks

   1. Correct option: (b) Increase the current flowing through the coil+1

   Answer: (b)
4. Q4Multiple choice·1 mark
   Which of the following statements correctly describes the significance of a tangent drawn at any point on a magnetic field line?

   1. (a)It represents the path taken by a neutral point.
   2. (b)It gives the magnitude of the magnetic field at that point.
   3. (c)It indicates the direction of the magnetic field at that point.
   4. (d)It shows the direction of the gravitational force on the magnet.
   Show answer and step marks

   1. Correct option: (c) It indicates the direction of the magnetic field at that point.+1

   Answer: (c)
5. Q5Long answer·4 marks
   (a) State two observations that provide evidence for the existence of the Earth's magnetic field. [2] (b) State the direction in which the Earth's magnetic field lines run outside the Earth's surface. [1] (c) Explain why the magnetic field lines of the Earth are considered to be parallel and uniform in a limited region on the Earth's surface. [1]
   Show answer and step marks

   1. (a) First observation, any one of: a freely suspended magnet (or compass needle) always comes to rest in the geographic north-south direction; a soft iron bar buried in the earth in the north-south direction becomes magnetised; neutral points are obtained when the magnetic field lines of a bar magnet are plotted, because the Earth's field cancels the magnet's field there; or any other valid observation.+1
   2. (a) Second observation, a different one from the same list.+1
   3. (b) Outside the Earth's surface the field lines run from geographic South to geographic North.+1
   4. (c) Because the Earth is of enormous size, its magnetic poles are very far from any small local region, so the field lines there are almost straight, parallel and uniform.+1

   Answer: (a) Any two of: a freely suspended magnet rests in the N-S direction; a soft iron bar buried N-S becomes magnetised; neutral points appear when a bar magnet's field is plotted. (b) From geographic South to geographic North. (c) The Earth is so large that over a small region its field lines are nearly straight, parallel and uniform.

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