Question 1

Fill in the blanks:
(i) The solution used in a Voltaic cell is called ______.
(ii) A current carrying coil behaves like a ______.

Accepted Answer

(i) The solution used in a Voltaic cell is called electrolyte.
(ii) A current carrying coil behaves like a magnet. — A Voltaic cell contains an electrolyte solution which allows the flow of ions and thus generates electric current. A current carrying coil produces a magnetic field and behaves like a magnet, known as an electromagnet.

Question 2

Choose the correct option:
(i) Dry cells are less portable compared to Voltaic cells. (True/False)
(ii) A coil becomes an electromagnet only when electric current flows through it. (True/False)
(iii) An electromagnet, using a single cell, attracts more iron paper clips than the same electromagnet with a battery of 2 cells. (True/False)

Accepted Answer

(i) False. Dry cells are more portable compared to Voltaic cells because they are compact and sealed.
(ii) True. A coil behaves like an electromagnet only when electric current flows through it.
(iii) False. An electromagnet with a battery of 2 cells attracts more iron paper clips than with a single cell because more current produces a stronger magnetic field. — Dry cells are portable due to their compact design. The magnetic effect arises only when current flows through the coil. More cells in series increase current and hence the strength of the electromagnet.

Question 3

An electric current flows through a nichrome wire for a short time.
(i) The wire becomes warm.
(ii) A magnetic compass placed below the wire is deflected.
Choose the correct option:
(a) Only (i) is correct
(b) Only (ii) is correct
(c) Both (i) and (ii) are correct
(d) Both (i) and (ii) are not correct

Accepted Answer

Correct option is (c) Both (i) and (ii) are correct.
Explanation:
(i) When electric current flows through the nichrome wire, it heats up due to the heating effect of current.
(ii) The current also produces a magnetic field around the wire, which deflects the magnetic compass needle placed nearby. — The heating effect causes the wire to become warm, and the magnetic effect causes the compass needle to deflect.

Question 4

Match the items in Column A with those in Column B.

|  Column A |   | Column B  |   |
| --- | --- | --- | --- |
|  (i) | Voltaic cell | (a) | Best suited for electric heater  |
|  (ii) | Electric iron | (b) | Works on magnetic effect of electric current  |
|  (iii) | Nichrome wire | (c) | Works on heating effect of electric current  |
|  (iv) | Electromagnet | (d) | Generates electricity by chemical reactions  |

Accepted Answer

Matching pairs:
(i) Voltaic cell - (d) Generates electricity by chemical reactions
(ii) Electric iron - (a) Best suited for electric heater
(iii) Nichrome wire - (c) Works on heating effect of electric current
(iv) Electromagnet - (b) Works on magnetic effect of electric current — Voltaic cells generate electricity chemically. Electric irons use heat, so best suited for electric heater. Nichrome wire heats up due to current (heating effect). Electromagnets work due to magnetic effect of current.

Question 5

Nichrome wire is commonly used in electrical heating devices because it
(i) is a good conductor of electricity.
(ii) generates more heat for a given current.
(iii) is cheaper than copper.
(iv) is an insulator of electricity.

Accepted Answer

Correct reasons are:
(ii) Nichrome wire generates more heat for a given current due to its high resistivity.
(iii) It is cheaper than copper.
Explanation:
(i) is incorrect because nichrome is not a very good conductor compared to copper.
(iv) is incorrect because nichrome is a conductor, not an insulator. — Nichrome's high resistance causes more heat generation, making it suitable for heating devices. It is also cost-effective compared to copper.

Question 6

Electric heating devices (like an electric heater or a stove) are often considered more convenient than traditional heating methods (like burning firewood or charcoal). Give reason(s) to support this statement considering societal impact.

Accepted Answer

Electric heating devices are more convenient because:
- They provide instant heat and can be switched on/off easily.
- They do not produce smoke or harmful gases, thus reducing air pollution.
- They are safer and cleaner compared to burning firewood or charcoal.
- They save time and effort in fuel collection and preparation.
- They reduce deforestation and environmental degradation caused by cutting wood. — Electric heaters are efficient, clean, and environmentally friendly, improving health and reducing pollution in society.

Question 7

Look at the Fig. 4.4a. If the compass placed near the coil deflects: (i) Draw an arrow on the diagram to show the path of the electric current. (ii) Explain why the compass needle moves when current flows. (iii) Predict what would happen to the deflection if you reverse the battery terminals.

Accepted Answer

(i) The arrow should show the direction of current flowing through the coil as per the circuit.
(ii) The compass needle moves because the electric current in the coil produces a magnetic field which affects the magnetic needle.
(iii) If the battery terminals are reversed, the direction of current reverses, and the compass needle deflects in the opposite direction. — Electric current produces magnetic field around the coil, influencing the compass needle. Reversing current reverses magnetic field direction.

Question 8

Suppose Sumana forgets to move the switch of her lifting electromagnet model to OFF position (in introduction story). After some time, the iron nail no longer picks up the iron paper clips, but the wire wrapped around the iron nail is still warm. Why did the lifting electromagnet stop lifting the clips? Give possible reasons.

Accepted Answer

Possible reasons:
- The iron nail may have become demagnetized due to heating caused by current.
- The current might have reduced due to battery drainage or loose connections.
- The iron nail may have lost its magnetic properties temporarily due to continuous heating.
- The wire being warm indicates current is still flowing, but the magnetic strength has decreased. — Heating can reduce magnetism of iron nail; battery or connection issues can reduce current and magnetic field strength.

Question 9

In Fig. 4.12, in which case the LED will glow when the switch is closed?

(a)

(b)
Fig. 4.12

Accepted Answer

The LED will glow in case (b) when the switch is closed.
Explanation:
LEDs are polarized devices and will glow only if connected in correct polarity. In figure (b), the LED is connected in correct direction allowing current flow when switch is closed. — LED glows only when forward biased; figure (b) shows correct polarity connection.

Question 10

Neha keeps the coil exactly the same as in Activity 4.4 but slides the iron nail out, leaving only the coiled wire. Will the coil still deflect the compass? If yes, will the deflection be more or less than before?

Accepted Answer

Yes, the coil will still deflect the compass because current flowing through the coil produces a magnetic field.
However, the deflection will be less than before because the iron nail acts as a core and strengthens the magnetic field of the coil. — Iron core increases magnetic field strength; without it, magnetic field is weaker causing less deflection.

Question 11

We have four coils, of similar shape and size, made up from iron, copper, aluminium, and nichrome as shown in Fig. 4.13.

When current is passed through the coils, compass needles placed near the coils will show deflection.

(i) Only in circuit (a)
(ii) Only in circuits (a) and (b)
(iii) Only in circuits (a), (b), and (c)
(iv) In all four circuits

Accepted Answer

Correct option is (iv) In all four circuits.
Explanation:
When current flows through any coil, it produces a magnetic field that can deflect a compass needle regardless of the coil material. However, the strength of deflection may vary depending on the material's magnetic properties. — Electric current produces magnetic field in all coils; compass deflects in all cases.

Question 12

Which scientist discovered that an electric current produces a magnetic field around a conductor, causing a compass needle to deflect?

Accepted Answer

Hans Christian Oersted — Hans Christian Oersted discovered in 1820 that an electric current flowing through a wire produces a magnetic field around it, evidenced by the deflection of a nearby compass needle. This was the first demonstration of the link between electricity and magnetism.

Question 13

When the electric current flows through a straight conductor placed above a magnetic compass, what happens to the compass needle?

Accepted Answer

It deflects from its original direction — When current flows through the conductor, it produces a magnetic field around it. This magnetic field causes the compass needle, which is a tiny magnet, to deflect from its original north-south direction. When the current stops, the needle returns to its original position.

Question 14

What is the term used to describe the invisible region around a magnet or a current-carrying wire where its magnetic effect can be detected?

Accepted Answer

magnetic field — The magnetic field is the region around a magnet or a current-carrying wire where magnetic forces can be detected, such as by the deflection of a compass needle. It is invisible but can be observed through its effects on magnetic materials.

Question 15

In Activity 4.2, when a wire is tightly wrapped around an iron nail and connected to a cell, what happens when the current flows through the wire?

Accepted Answer

The nail attracts iron paper clips temporarily — When current flows through the coil of wire wrapped around the iron nail, it produces a magnetic field that magnetizes the nail temporarily, turning it into an electromagnet. This temporary magnet attracts iron paper clips. When the current stops, the magnetic effect disappears and the clips fall off.

Electricity: Magnetic and Heating Effects

Electricity: Magnetic and Heating Effects — Study Notes

Probe and ponder

4.1 Does an Electric Current Have a Magnetic Effect?

4.1.1 Electromagnets

Practice Questions — Electricity: Magnetic and Heating Effects

All 13 Chapters in Curiosity