Students rely on Class 8 Science Extra Questions and Class 8 Curiosity Chapter 4 Extra Question Answer Electricity Magnetic and Heating Effects to help self-study at home.
Class 8 Science Chapter 4 Electricity Magnetic and Heating Effects Extra Questions
Class 8 Science Chapter 4 Extra Questions on Electricity Magnetic and Heating Effects
Electricity Magnetic and Heating Effects Class 8 Very Short Question Answer
Question 1.
In a science project, Bhanu used a plastic rod inside the coil instead of an iron rod. What result do you expect and Why? (Competency Based Que.)
Answer:
The electromagnet would be weak or may not work, because plastic is not a magnetic material like iron.
Question 2.
Can the poles of an electromagnet be reversed? If yes, how?
Answer:
Yes, by reversing the direction of current in the coil, the poles of the electromagnet also get reversed.
Question 3.
State one difference between a bar magnet and an electromagnet.
Answer:
A bar magnet is permanent, while an electromagnet works only when electric current flows through it, it is not a permanent magnet.
Question 4.
Maya saw a crane lifting scrap metal using a large magnet at a junkyard. What kind of magnet was it most likely using?
Answer:
It was most likely using a strong electromagnet that works on the principle of magnetic effect of the electric current.
Question 5.
What change can be made in a coil to make an electromagnet stronger?
Answer:
We can increase the number of turns in the coil or use a stronger current to make the electromagnet stronger.
Question 6.
What happens to the heat produced if we increase the electric current in a wire?
Answer:
The heat produced increases as current increases, because heat is proportional to the square of current.
Question 7.
Can increasing the thickness of the wire in an electric heater reduce the heat produced?
Answer:
Yes, thicker wires have lower resistance, so less heat is generated.
Question 8.
Why does a geyser stop working when there is a fault in the heating element?
Answer:
The heating element is responsible for producing heat, if damaged, water cannot be heated.
Question 9.
Why does an electric bulb’s filament glow but the wire connected to it doesn’t?
Answer:
The filament has higher resistance, so it heats up and glows more than the connecting wire.
Question 10.
Why does a remote control stop working even though the batteries are physically intact?
Answer:
The chemicals inside the battery get used up, so it can no longer produce electricity.
Question 11.
In a dry cell, which part acts as the positive terminal and which part acts as the negative terminal?
Answer:
The carbon rod is the positive terminal and the zinc container is the negative terminal.
Question 12.
What is the main difference between a dry cell and a voltaic cell in terms of design?
Answer:
A dry cell uses a paste-like electrolyte, while a voltaic cell uses a liquid solution.
Question 13.
Aditya found some used batteries at home. Why should he not throw them in the dustbin?
Answer:
They contain harmful chemicals and should be disposed of at e-waste recycling centres.
Electricity Magnetic and Heating Effects Class 8 Short Question Answer
Question 1.
In the frog-leg experiment, Galvani noticed that a dead frog’s leg kicked when touched with two different metals. What did this observation lead to? (Competency Based Que.)
Answer:
Galvani’s frog-leg experiment showed that muscle motion could be triggered using metals, sparking the idea of electric current. This inspired Alessandro Volta to invent the first electric cell, proving electricity came from metals and chemicals.
Question 2.
Why is it important to use only for a short time the electric cell in the electromagnet activities?
Answer:
Keeping the electric circuit ON for too long during electromagnet activities can drain the cell’s energy quickly, making it weak. The wires may also get heated, which can be unsafe and may damage the circuit. Continuous current can reduce the strength of the electromagnet and shorten the battery’s life. To make the setup last longer and work safely, it is better to switch OFF the current after a short time.
Question 3.
What is the magnetic effect of electric current and how was it discovered?
Answer:
The magnetic effect of electric current means that when electric current flows through a wire, it creates a magnetic field around it. This was discovered by Hans Christian Oersted when he observed that a magnetic compass needle moved when placed near a current-carrying wire, showing the link between electricity and magnetism.
Question 4.
Why is nichrome used as a heating element in electrical appliances?
Answer:
Nichrome is used because it gets hot easily when electric current passes through it, but it doesn’t melt quickly. It has high resistance and can handle heat for a long time. That’s why it is used in devices like electric heaters, toasters and irons to produce heat safely.
Question 5.
Why should batteries be recycled and not thrown in dustbins? (Competency Based Que.)
Answer:
Batteries contain chemicals and metals like lead, lithium, and cadmium that can harm the environment if thrown in normal trash. These materials can leak into the soil or cause fires. Recycling helps recover useful metals and prevents pollution. It’s safer for both people and the planet.
Question 6.
Why are scientists working on developing solid-state batteries? (Competency Based Que.)
Answer:
Solid-state batteries use solid electrolytes instead of liquids or paste. They are safer, charge faster and last longer. Scientists are developing them to make batteries more reliable and efficient for future use in electronics, electric vehicles and clean energy systems.
Question 7.
What was the main difference in understanding between Galvani and Volta regarding the source of electricity?
Answer:
Galvani believed the electricity came from inside the frog’s body, while Volta thought it came from the interaction between different metals. Volta’s experiments later confirmed that it was the metals and the electrolyte that produced electricity, not the animal body.
Question 8.
Why is there a global effort to recycle lithium-ion batteries? (Competency Based Que.)
Answer:
Lithium-ion batteries use rare and valuable metals like lithium and cobalt, which are only found in certain parts of the world. Recycling helps conserve these materials, reduces environmental damage from mining and supports the growing demand for batteries in clean energy and electric transport.
Question 9.
You insert an iron nail into a paper tube coil connected to a battery. What difference do you notice compared to the coil without the nail?
Answer:
The iron nail increases the magnetic strength of the coil, making it a stronger electromagnet. The compass deflection near the coil becomes greater, and more paper clips can be picked up. Without the nail, the magnetic effect is weaker.
Question 10.
What happens when you pass electric current through a steel spoon wrapped with wire? Try it for a few seconds. Does the spoon feel warm? Why does this happen?
Answer:
When electric current flows through the wire wrapped around the steel spoon, it heats up due to the heating effect of current. This heat is transferred to the spoon, making it warm. This activity shows how electric energy changes into heat energy in conductors.
Electricity Magnetic and Heating Effects Class 8 Long Question Answer
Question 1.
What is the magnetic effect of electric current? Explain how a crane uses this principle to lift heavy scrap metal. Also mention two ways to increase the strength of an electromagnet.
Answer:
When electric current flows through a wire, it produces a magnetic field around it. This is known as the magnetic effect of electric current.
In junkyards, electromagnetic cranes are used to lift and move heavy pieces of scrap metal.
When electric current flows through the coil of the electromagnet, it produces a strong magnetic field that pulls metal objects toward it.
Once the current is switched off, the magnetic field disappears, allowing the metal to be released easily.
This on-off control helps the crane pick up and drop metal objects quickly and safely.
Ways to Increase the Strength of an Electromagnet
- Increase the number of turns in the coil.
- Increase the amount of electric current passing through the coil.
Question 2.
Ria observed that her electric iron gets hot quickly
when plugged in, while the wires supplying current to it remain cool. (Competency Based Que.)
(i) Explain why the heating element inside the iron gets hot but the wire doesn’t.
(ii) What are the key factors that affect how much heat is produced in a wire?
(iii) Why is nichrome used in the heating element instead of copper?
(iv) What safety measures must be taken while using heating appliances at home?
Answer:
(i) The heating element in an electric iron is made of nichrome, which has high resistance. This resistance causes it to get hot when current flows. The supply wires are made of copper, which has very low resistance, so they stay cool.
(ii) The amount of heat produced depends on the resistance of the wire, the strength of the current, and the time for which current flows.
(iii) Nichrome is used because it gets hot quickly without melting and can withstand high temperatures. Copper, though a good conductor, has low resistance and is not suitable for heating.
(iv) One should avoid using damaged or thin wires, never leave heating devices on for too long, and keep flammable materials away to prevent fire hazards.
Question 3.
As the world moves towards electric vehicles and portable electronics, lithium-ion batteries have become extremely important. Explain what makes lithium-ion batteries widely used in modern devices. What are the major concerns related to the materials used in these batteries, and how can recycling help solve these problems?
Answer:
Lithium-ion batteries are popular because they are lightweight, rechargeable, and can store a lot of energy. This makes them ideal for use in mobile phones, laptops, and electric vehicles.
However, these batteries use rare materials like lithium and cobalt, which are limited in supply. Mining these materials can also harm the environment and involve unethical practices in some regions.
To reduce this impact, recycling used batteries is important. It helps recover valuable materials and prevents pollution caused by improper disposal.
Electricity Magnetic and Heating Effects Class 8 Case Based Questions
Question 1.
Riya noticed her old phone battery wasn’t holding charge for long. Her teacher explained that most modern devices use lithium-ion batteries, which are rechargeable. The teacher also said these batteries contain metals like lithium and cobalt, and must be disposed of safely as they can harm the environment.
Riya learned about recycling batteries through e-waste collection centres.
Answer the following questions
(i) What type of battery is used in most modern devices like phones and laptops?
(ii) Why should used lithium-ion batteries not be thrown in regular dustbins?
(iii) Name two metals commonly found in lithium-ion batteries.
Answer:
(i) Lithium-ion (Li-ion) batteries.
(ii) Because they contain harmful chemicals and metals that can pollute the environment or cause fires.
(iii) Lithium and cobalt.
Skill Based Questions
Question 1.
A student sets up a beaker containing 200 mL of water and a digital thermometer. She immerses a heating coil connected to a battery into the water and switches on the current. After 5 minutes, the temperature recorded is 30 °C. She repeats the experiment, but this time she uses a heating coil made from a different material with the same length as before. After 5 minutes, the temperature of water reads only 24°C. (Experimental Skill)
Which conclusion can be drawn from this experiment?
(a) The mass of water affects the temperature rise.
(b) Changing the material of the heating coil affects the heat produced.
(c) Using a thicker wire produces more heat.
(d) Increasing the current reduces heating.
Question 2.
Compare the magnetic strength of an air-core electromagnet versus one with an iron core. Explain the science behind the difference. (Analysts skin)
Question 3.
A student claims that a longer wire always produces more heat than a shorter one. Do you agree? Justify your answer by considering all the factors on which heating depends. (Analytical skin)
Question 4.
(i) As shown in the above picture, why does the circuit acquire magnetism?
(ii) How can the magnetic strength of an electromagnet can be increased?
(iii) Name two commericially used devices that work on electromagnetism?
Electricity Magnetic and Heating Effects Extra Questions for Practice
Very Short Answer Type Questions
Question 1.
Why do batteries stop working even when they are not used continuously?
Question 2.
Can a magnet be switched on and off? If yes, name it.
Question 3.
How does using an iron core improve the efficiency of an electromagnet?
Question 4.
What type of battery is mostly used in smartphones and electric vehicles today?
Question 5.
Why does the needle of a magnetic compass move when placed near a current-carrying wire?
Short Answer Type Questions
Question 1.
How can we reverse the poles of an electromagnet? What change must be made in the setup?
Question 2.
In what way is the heating effect of current useful in an electric geyser?
Question 3.
Why is an electromagnet preferred in cranes over permanent magnets?
Question 4.
Why is it safer to use thicker wires in household electric circuits instead of thin ones?
Long Answer Type Questions
Question 1.
Explain the working of an electromagnet with the help of an activity. What materials are needed to make a simple electromagnet? Describe the steps to create one.
Question 2.
Compare dry cells, Voltaic cells, and rechargeable batteries.