CBSE Class 10 Science Magnetic Effects of Electric Current VBQs Set 05

This Class 10 Science page collects 8 real-life and case based questions on Magnetic Effects of Electric Current, each answered step by step with a simple-words summary and a teacher's note. The questions connect field lines, electromagnets, magnetism in the human body, induced current in road loops, bar magnet and coil experiments and household AC with everyday situations.

Real-Life and Case Based Questions

Question 1. When an electric current is passed through any wire, a magnetic field is produced around it. Then why does an electric iron connecting cable not attract nearby iron objects when electric current is switched on through it?
Answer:
The magnetic field produced by the current in the cable is very weak, because the currents used in the cable are small compared with those needed for noticeable magnetism.
The two wires inside the cable carry current in opposite directions (live and neutral), so their magnetic fields almost cancel outside the cable.
So the cable cannot attract iron objects; an electromagnet needs a coil with many turns and an iron core to give a strong field.
In simple words: The field of a single cable is too weak, and the opposite currents cancel it.

Teacher's Note:
1. Give the cancellation argument in two-wire cables.
2. Compare with a solenoid with an iron core.

Question 2. How is magnetism produced inside the human body?
Answer:
Inside the human body, ions move and form tiny ionic currents. Every electric current produces a magnetic field.
The magnetic field produced is quite significant in the brain and the heart, where the electrical activity is strong.
In simple words: Moving ions in the body make weak magnetic fields, most in the heart and brain.

Teacher's Note:
1. Link magnetism with moving charges.
2. Name the two organs.

Question 3. If your metal car moves over a wide, closed loop of wire embedded in a road surface, will the magnetic field of the Earth within the loop be altered? Will this produce a current pulse? Can you think of a practical application for this at a traffic intersection?
Answer:
Yes. The metal car changes the magnetic field of the Earth within the loop.
This change in the field induces a current in the wire loop, so a current pulse is produced (electromagnetic induction).
Application: the pulses are used at a traffic intersection to detect waiting vehicles, so that the colour of the traffic light can change.
In simple words: A car passing over a wire loop induces a current pulse that controls the traffic light.

Teacher's Note:
1. Name the phenomenon of electromagnetic induction.
2. Describe the use in daily life.

Question 4. State the use of magnetic field produced inside a solenoid.
Answer:
The strong magnetic field inside a solenoid is used to magnetise a piece of soft iron placed in it, which forms a strong but temporary magnet called an electromagnet.
Electromagnets are used in a wide variety of instruments, and for lifting heavy iron objects.
In simple words: A solenoid with an iron core makes a switchable magnet, used to lift heavy iron objects.

Teacher's Note:
1. Name the electromagnet.
2. Mention the daily-life use of lifting iron.

Question 5. How is the type of current that we receive in a domestic circuit different from the one that runs a clock?
Answer:
The current in a domestic circuit is alternating current (A.C.), which reverses its direction periodically.
The current that runs a clock (from a cell) is direct current (D.C.), which always flows in one direction.
In simple words: Mains is AC; the clock runs on a cell, which gives DC.

Teacher's Note:
1. Name each type of current.
2. Say how the direction behaves.

Question 6. A bar magnet is moved in and out of a coil connected to a sensitive centre zero meter. The meter needle swings to the left when the magnet is moving towards the coil. (i) How does the needle behave when the bar magnet is at rest? (ii) How does the needle behave when the bar magnet is at rest and the coil is moving away from the magnet? (iii) In which condition does the meter needle swing to the left? (iv) Which phenomenon is involved in this? (v) Give two applications based on the given phenomenon.
Answer:
(i) The needle stays at zero, because no current is induced when there is no relative motion.
(ii) The needle swings to the right, because the coil moving away from the magnet produces a current opposite to that when the magnet moves towards the coil.
(iii) When the magnet moves towards the coil (or the coil moves towards the magnet).
(iv) Electromagnetic induction.
(v) Electric generator and the dynamo of a bicycle.
In simple words: The needle moves only when the magnet and coil move relative to each other.

Teacher's Note:
1. Answer each part in one line.
2. Direction of the swing depends on whether the magnet goes in or out.

Question 7. A child fixes a sheet of white paper on a drawing board and places a bar magnet at the centre. He sprinkles iron filings uniformly around it with a salt-sprinkler and taps the board gently. (i) What type of material is placed on the white paper? (ii) Why do the iron filings arrange in such a pattern? (iii) What should we call the region in which the magnetic force can be detected? (iv) What do the lines in the pattern demonstrate? (v) Does the degree of closeness of the field lines relate to something?
Answer:
(i) A magnet (a bar magnet) is placed on the paper.
(ii) The magnet exerts a force on the iron filings in the region around it, and this force arranges them in a pattern.
(iii) The region is called the magnetic field.
(iv) The lines are the magnetic field lines, which show the region in which the force of the magnet can be detected.
(v) Yes. The closeness of the lines shows the relative strength of the field; where the lines are crowded, the field is stronger.
In simple words: Iron filings line up along the magnetic field lines of the magnet.

Teacher's Note:
1. Name the terms: magnetic field and field lines.
2. Closer lines mean a stronger field.

Question 8. Jay performs an experiment by using two different coils of copper wire having a different number of turns. He inserted them over a non-conducting cylindrical roll. Then he connects coil-1, having a large number of turns, in series with a battery and plug key, and the other coil-2 with a galvanometer. As he plugs the key, he observes some deflection in the galvanometer. (i) Why is there deflection in the galvanometer when the key is inserted in the circuit? (ii) When is there a flow of induced current through a coil? (iii) Jay disconnected coil-1 from the battery and noted the observation: the needle momentarily moves but in the opposite direction. Justify the statement. (iv) When will the induced current be found to be highest?
Answer:
(i) When the key is plugged, the current in coil-1 changes from zero, so the magnetic field associated with it changes. This changes the field linked with coil-2 and a current is induced in it.
(ii) An induced current flows in a coil only when there is a change in the magnetic field linked with the coil.
(iii) When coil-1 is disconnected, its current falls to zero and the field changes in the opposite sense, so the current induced in coil-2 flows in the opposite direction and the needle moves the other way, again only momentarily.
(iv) The induced current is highest when the direction of motion of the conductor is at right angles to the magnetic field.
In simple words: Switching the current on or off changes the field and induces a short current in the other coil.

Teacher's Note:
1. The deflection lasts only while the field is changing.
2. Opposite change gives opposite direction.