Start by reviewing these Class 8 Science Curiosity Solutions Chapter 4 Electricity Magnetic and Heating Effects Question Answer to strengthen your knowledge.
Class 8 Science Curiosity Chapter 4 Question Answer
Class 8 Science Ch 4 Electricity Magnetic and Heating Effects Question Answer
Class 8 Science Chapter 4 Electricity Magnetic and Heating Effects Question Answer (InText)
Question 1.
Can we use electric current to make a magnet? (Page 49)
Answer:
Yes. When electric current flows through a coil of wire, it produces magnetic effect and makes the coil act like a magnet. This temporary magnet is called an electromagnet.
Question 2.
Does electromagnet have two poles like a bar magnet? (Page 50)
Answer:
Yes, an electromagnet has a north and a south pole just like a bar magnet. You can find them using a compass or another magnet.
Question 3.
Are electromagnets also used in real life, for lifting Objects? (Page 52)
Answer:
Yes, strong electromagnets are used in scrapyard cranes to pick up and move heavy iron and steel items safely.
Question 4.
While doing activity for electromagnet, did you also notice that the wire ends got warm? Why would that happen? (Page 52)
Answer:
Yes, the ends of wire get warm because electric current faces resistance in the wire, some electrical energy converts into heat. This is the heating effect of current.
Question 5.
What is inside these cells and batteries that produces electricity? (Page 55)
Answer:
They contain two different metal electrodes and an electrolyte (liquid or paste). A chemical reaction which causes the electric current.
Question 6.
Can we also make our own Voltaic cell using easily available materials? (Page 56)
Answer:
Yes, you can make a simple cell using lemons, copper strips, and iron nails. The acid in the lemon juice acts as the electrolyte to produce electric current.
Electricity Magnetic and Heating Effects Class 8 Questions and Answers (Exercise)
Question 1.
Fill in the blanks
(i) The solution used in a Voltaic cell is called ………………………..
(ii) A current carrying coil behaves like a ………………………..
Answer:
(i) electrolyte
(ii) magnet
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)
Answer:
(i) False
(ii) True
(iii) False
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
Answer:
(c) Both (i) and (ii) are correct.
The nichrome wire heats up because of the heating effect of electric current. The compass needle deflects because the flow of current produces magnetic effect around the wire (magnetic effect).
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 |
Answer:
(i) – (d), (ii) – (c), (iii) – (a), (iv) – (b)
| Column A | Column B |
| (i) Voltaic cell | (d) Generates electricity by chemical reactions |
| (ii) Electric iron | (c) Works on heating effect of electric current |
| (iii) Nichrome wire | (a) Best suited for electric heater |
| (iv) Electromagnet | (b) Works on magnetic effect of electric 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.
Answer:
(ii) generates more heat for a given current because nichrome has a much higher electrical resistance than metals like copper, so when the same current flows through it, more electrical energy is converted into heat.
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.
Answer:
Electric heating devices are cleaner and safer than burning firewood or charcoal because they do not produce harmful smoke. They are easier to use, just switch on, and you get instant heat without the effort of gathering fuel. This saves time and reduces indoor air pollution, which is better for everyone’s health. Electric heaters also help protect trees and the environment by cutting down on firewood use.
Question 7.
Look at the figure. 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.
Answer:
(i) The electric current flows from the positive end of the battery, up through the wire at A around the coil from A to B, and back down through the wire at B to the negative end of the battery.
(ii) When current flows in the coil, it makes a magnetic field. This magnetic field affects the compass and makes its needle move.
(iii) If you reverse the battery connections, the magnetic field around the. coil will reverse its direction, so the compass needle will deflect in the opposite way.
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.
Answer:
The lifting electromagnet stopped working because the battery got weak or used up due to continuous current flow. When the battery becomes weak, the current in the wire becomes too low to create a strong magnetic field. That’s why the iron nail can no longer lift the clips. But the wire still feels warm because a small current is still passing through it.
Question 9.
In Fig. below, in which case the LED will glow when the switch is closed?
Answer:
The LED will glow in Fig. (a) where lemon juice is used. To make the LED glow, we need a solution that allows electric current to pass through easily. Lemon juice is a good conductor of electricity. Pure water in Fig. (b) does not conduct electricity, so the LED does not glow.
Question 10.
Neha keeps the coil exactly the same as in Activity 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?
Answer:
Yes, the coil will still deflect the compass because current is flowing through it, which creates a magnetic field. But since the iron nail is removed, the magnetic effect will be weaker than before. The iron nail increases the strength of the electromagnet. So without the nail, the deflection will be less.
Question 11.
We have four coils, of similar shape and size, made up from iron, copper, aluminium, and nichrome as shown in Fig. below.
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
Answer:
(iv) In all four circuits
All the materials—iron, copper, aluminium and nichrome are good conductors of electricity. So, when current flows through each coil, it creates a magnetic field around it. That’s why the compass needle will deflect near all the four coils.
Class 8 Science Chapter 4 Question Answer (Activities)
Activity 1 (Pages 47 – 48)
Aim To observe the magnetic effect of the electric current using the compass needle.
Materials Required
Magnetic compass, electric cell, cell holder, two drawing pins, safety pin, two iron nails, one long and one short connecting wire, two small cardboard pieces.
Procedure
- Make a simple switch using a cardboard piece, two drawing pins and a safety pin and place the electric cell in the cell holder.
- Fix two nails on one cardboard piece as shown in Fig (a). Stretch the longer wire between the nails so it stays slightly above the surface. Connect one end of this wire to the cell holder and the other end to the switch.
- Use the shorter wire to connect the remaining terminals of the switch and the cell holder, completing the circuit.
- Place the magnetic compass directly under the stretched wire as shown in fig (a). Now, turn the switch ON and observe the compass needle as shown in fig (b).
- Turn the switch OFF and again observe the needle.
- Repeat switching between ON and OFF a few times and watch how the compass needle reacts each time.
Conclusion
When the current flows, the compass needle gets deflected. When the current stops, the needle returns to its original position. This shows that electric current produces a magnetic effect.
Viva questions
- Why does the needle return to its original position when the current is switched off?
- If the wire is placed farther away from the compass, will the deflection increase or decrease?
- What change will you observe if the current in the wire is increased?
Activity 2 (Page 49)
Aim
To make an electromagnet using an iron nail and observe its magnetic property.
Materials Required
Flexible insulated wire (about 50 cm), iron nail, electric cell, adhesive tape, iron paper clips.
Procedure
- Wrap the wire tightly around the iron nail to make a coil as shown in fig (a). Secure the coil using adhesive tape.
- Connect both ends of the wire to the terminals of the cell.
- Briefly bring the nail near the iron paper clips and try to lift them.
- Disconnect the wire and check if the clips still stick.
Conclusion
The nail acts like a magnet when current flows through the coil. The magnetic effect disappears when the current is stopped.
Viva Questions
- What is the difference between a bar magnet and the electromagnet you made?
- How can you make the electromagnet stronger in this setup?
- How can you check if an electromagnet is working without using paper clips?
Activity 3 (Pages 49 – 50)
Aim
To observe how a coil with and without an iron core affects magnetic compasses and attracts objects.
Materials Required
Flexible insulated wire (about 100 cm), chart paper, iron nail, electric cell, two magnetic compasses, adhesive tape, and a few iron/steel paper clips.
Procedure
- Roll a piece of chart paper into a pencil-sized cylinder and secure it with tape and wind about 50 tight turns of the wire over the cylinder to form a coil as shown in fig (a).
- Fix the wire in place with adhesive tape so it does not loosen.
- Place one magnetic compass near each end of the coil as shown in fig (b). Connect both ends of the coil to the electric cell as shown in fig (c) and observe the compass needles.
- Disconnect the wire from the cell and note whether the needles return to normal.
- Now, insert an iron nail inside the paper coil as shown in fig (d). Reconnect the wire to the cell and again observe the compass needles.
- Bring iron paper clips near the ends of the coil and observe if they get attracted.
Conclusion
The compass needles deflect when current flows through the coil, showing a produced. Inserting the iron nail strengthens the magnetic field and allows the coil to attract paper clips.
Viva Question
- Why does the coil alone attract fewer paper clips compared to the coil with the iron nail?
- What would happen if we increased the number of turns in the coil?
- How does inserting an iron nail inside the coil change the behaviour of the compass needles?
Activity 4 (Pages 50 – 51)
Aim
To identify the north and south poles of an electromagnet.
Materials Required
Electromagnet made in Activity 3, magnetic compass, electric cell, connecting wires.
Procedure
- Take the coil used in Activity 3 and label its two ends as A and B. Place a magnetic compass near end A of the coil as shown in fig (a).
- Connect the coil to the cell and observe which end of the compass needle is attracted to end A
- If the north pole of the compass needle is attracted, then end A is the south pole of the electromagnet.
- Now move the compass near end B and repeat the same observation. Note which pole of the compass is attracted to end B to find its polarity.
Conclusion
An electromagnet has two poles-north and south, just like a bar magnet. The poles can be found using a magnetic compass.
Viva Questions
- What is the use of a magnetic compass in this activity?
- What will happen to the poles if we reverse the direction of current in the coil?
Activity 5 (Pages 52 – 53)
Aim
To observe and compare the heating of a nichrome wire when electric current flows through it.
Materials Required
Cardboard (≈ 10 cm × 10 cm), two iron nails, nichrome wire (0.3 mm gauge, ≈10 cm), electric cell with holder, switch, connecting wires.
Procedure
- Fix the two nails upright on the cardboard, about 5 cm apart. Tie the ends of the nichrome wire to the nails so it is stretched tightly.
- Connect one nail to the cell holder, the other to the switch, and complete the circuit with a connecting wire (switch OFF) as shown in the fig (a).
- Carefully touch the nichrome wire and note how it feels at room temperature.
- Turn the switch ON for about 30 seconds, then turn it OFF. Quickly touch the wire (briefly) and note the change.
- Repeat switching ON and OFF once more to confirm your observations.
Conclusion
The nichrome wire feels warm only when current flows through it, showing that electrical energy is converted into heat. The wire cools down again once the current stops.
Viva Questions
- How can you increase the temperature of the nichrome wire in this setup?
- Why is it important not to keep the current ON for too long in this activity?
- What property of nichrome makes it suitable for heating applications?
Activity 6 (Page 56)
Aim
To build a simple battery using lemons and light up an LED.
Materials Required
5 – 6 lemons, copper wire strips (1 – 2mm thick), iron nails, one LED, and connecting wires.
Procedure
- Roll each lemon gently on a table to soften it without breaking the skin. Push one strip of copper wire and one iron nail into each lemon, keeping them about 2cm apart.
- Link the lemons in series by connecting the iron nail of the first lemon to the copper wire of the next and so on.
- Attach the free copper wire of the first lemon to the LED’s longer (positive) lead, and the free iron nail of the last lemon to the LED’s shorter (negative) lead.
- If the LED does not glow, swap its leads and observe again.
Conclusion
A string of lemon cells can produce enough voltage to light an LED. The copper and iron serve as electrodes and the lemon juice acts as the electrolyte. Connecting lemons in series increases the total voltage.
Viva Question
- Why are lemons connected in series rather than using just one?
- What will happen if the copper strip and iron nail do not touch directly inside the lemon?