Students can use Curiosity Class 8 Science Book Solutions Chapter 4 Electricity: Magnetic and Heating Effects Class 8 Question and Answer as a quick reference guide.
Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects Question Answer
Science Class 8 Chapter 4 Question Answer Electricity: Magnetic and Heating Effects
Electricity: Magnetic and Heating Effects Class 8 Question Answer (InText)
Question 1.
Probe and Ponder (Page 46)
- If we don’t have an electric lamp while making an electric circuit with an electric cell, is there any other way through which we can find out if current is flowing in the circuit?
- Is it possible to make temporary magnets? How can these be made?
- We can generate heat by burning fossil fuels and wood; but how is heat generated in various electrical appliances?
- How do we know if a cell or a battery is dead? Can all cells and batteries be recharged?
- Share your questions
……………………………………………………..
……………………………………………………..?
Answer:
(Questions may vary)
(i) Why does the element in a room heater or electric stove glow red hot when it is switched on?
(ii) How are very heavy objects lifted and displaced in industries or construction work?
Question 2.
Can we use electric current to make a magnet? (Page 49)
Answer:
Yes, electric current can be used to make a magnet. A current carrying coil behaves as a magnet known as electromagnet.
Question 3.
Does electromagnet also have two poles like a bar magnet? (Page 50)
Answer:
Yes, an electromagnet also has two poles like a bar magnet – North and South.
Question 4.
Are electromagnets also used in real life, for lifting objects? (Page 52)
Answer:
Yes, electromagnets are used in real life for lifting heavy objects, especially in scrap yards, factories etc.
Question 5.
While doing the activity 4.5 for electromagnet, did you also notice that the wire ends got warm? Why would that happen? (Page 52)
Answer:
The wire ends got warm because of the heating effect of the electric current.
Question 6.
What is inside these cells and batteries that produces electricity? (Page 55)
Answer:
Inside cells and batteries, there are two plates called electrodes and a liquid or paste called electrolyte. The chemical reaction takes place between the plates and electrolyte which produces electricity.
Question 7.
Can we also make our own Voltaic cell using easily available materials? (Page 56)
Answer:
Yes, we can make our own Voltaic cell using simple materials like copper, iron nails, and saltwater or lemon juice.
Question 8.
Why, after a year or two, the phone battery requires charging more often? (Page 57)
Answer:
Over time, the battery slowly wear out, reducing its efficiency, so it needs to be charged more often.
NCERT Class 8 Science Chapter 4 Question Answer Electricity: Magnetic and Heating Effects (Exercise)
Keep the curiosity alive (Pages 58-61)
Question 1.
Fill in the blanks:
(i) The solution used in a Voltaic cell is called ………..
(ii) The 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 option.
Question 4.
Match the items in Column A with their description in Column B.
Answer:
| Column A | Column B |
| (i) Voltaic cell (ii) Electric iron (iii) Nichrome wire (iv) Electromagnet |
(d) Generates electricity by chemical reactions (c) Works on heating effect of electric current (a) Best suited for electric heater (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:
(i) is a good conductor of electricity.
(ii) generates more heat for a given current.
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 more convenient than traditional heating methods like burning firewood or charcoal because they are clean, easy to operate, do not produce smoke or harmful gases, and are more energy efficient. These devices allow better control over temperature and reduce the risk of accidental fires. Also environment friendly as using electricity reduces the cutting of trees for firewood.
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.
Answer:
(i)
(ii) The compass needle moves when current flows through a wire because electric current produces a magnetic field around the wire.
(iii) Reversing the battery terminals will reverse the current direction, causing the compass needle to deflect in the opposite 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.
Answer:
The lifting electromagnet stopped working due to the following possible reasons:
- Overheating of the coil due to continuous current can reduce the magnetic properties of the iron nail.
- The insulation of the wire might have melted reducing current or causing a short circuit.
- Battery might have drained, so it could not supply enough current to make a strong electromagnet.
Question 9.
In Fig. 4.11, in which case the LED will glow when the switch is closed?
Answer:
The LED will glow in case (a) The setup with the lemon juice and copper strip.
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?
Answer:
Yes, the coil will still deflect the compass because a current carrying coil produces a magnetic field. The deflection will be less than before because the iron nail increases the strength of the magnetic field of the coil when placed inside the coil and makes the electromagnet stronger. When the iron nail is removed, the magnetic field becomes weaker, so the compass needle will show 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. 4.12.
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
Class 8 Electricity: Magnetic and Heating Effects Question Answer (Activities)
Activity 4.1: Let Us Investigate (Pages 47-48)
Aim: To demonstrate that an electric current flowing through a conductor produces a magnetic field around it.
Observation and conclusion: When the switch is moved to ‘ON’ position, the electric current flows through the wire, the needle of the magnetic compass placed under the wire moves or deflects. When the switch is moved to ‘OFF’ position the current stops, the needle of the magnetic compass goes back to its original position. This shows that a current passing through a wire creates a magnetic field around the wire, which affects the magnetic compass needle. This experiment proves that when an electric current flows through a conductor, it produces a magnetic field around it.
Activity 4.2: Let Us Explore (Page 49)
Aim: To explain that electric current can create a temporary magnetic effect.
Observation and conclusion: When the wire coil around the iron nail is connected to the electric cell, the nail attracts iron paper clips. When the current is stopped, the clips fall off. This shows that an electric current can create a temporary magnet.
Activity 4.3: Let Us Experiment (Pages 49-50)
Aim: To show that a current carrying coil acts as a temporary magnet called an electromagnet.
Observation and conclusion: When the coil is connected to the cell and current flows, the magnetic compass needle near the coil deflects. When an iron nail is inserted in the core of the coil, the deflection of the magnetic compass needle is much more. It also attracts iron clips. This shows that current carrying coil behaves like a temporary magnet called as electromagnet, and inserting an iron core makes it more stronger.
Activity 4.4: Let Us Investigate (Pages 50-51)
Aim: To prove that an electromagnet has two poles – North and South.
Observation and conclusion: In Fig. 4.4 (a), when the magnetic compass is placed near end A of the coil and the coil is connected to the cell, the north pole of the compass needle is attracted to end A . This means end A is the south pole of the electromagnet because we already know unlike poles of two magnets attract each other.
In Fig. 4.4(b), when the magnetic compass is placed near end B of the coil, the south pole of the compass is attracted, showing that end B is the north pole. This shows that an electromagnet has two poles, north and south, just like a regular magnet. The two ends of the coil have opposite polarity when current flows through it.
Activity 4.5: let us observe (pages 52-53)
Aim: To observe the heating effect of electric current in a conductor.
Observation and conclusion: When the switch is OFF, the nichrome wire feels normal when touched. When the switch is moved to ‘ON’ position for 30 seconds and then switched ‘OFF’, the nichrome wire feels warm. This shows that when an electric current flows through a conductor, it produces heat. This happens because nichrome offers resistance to the flow of current, which causes electrical energy to be converted into heat energy causing the wire to get warm or heated. This is called the heating effect of an electric current.
Activity 4.6: Let Us Construct (Page 56)
Aim: To show lemon juice produces electricity by converting chemical energy into electrical energy.
Observation and conclusion: When the copper wire and iron nail are inserted into the lemons and connected properly, the LED glows. This shows that the lemon juice acts as an electrolyte and the copper wire and iron nail act as electrodes. Together, they form a simple electric cell that produces a small electric current. This electric current is enough to light the LED. So, we conclude that chemical energy from the lemon can be converted into electrical energy. A glowing LED indicates that the cell is working and chemical energy is being converted into electrical energy.