In this page, we are providing Electric Current and Its Effects Class 7 Extra Questions and Answers Science Chapter 14 pdf download. NCERT Extra Questions for Class 7 Science Chapter 14 Electric Current and Its Effects with Answers will help to score more marks in your CBSE Board Exams.
Class 7 Science Chapter 14 Extra Questions and Answers Electric Current and Its Effects
Extra Questions for Class 7 Science Chapter 14 Electric Current and Its Effects with Answers Solutions
Electric Current and Its Effects Class 7 Extra Questions Very Short Answer Type
What is a battery?
When two or more cells are joined together, it is called a battery.
Name the effects of electric current.
- Heating effect
- Magnetic effect
- Chemical effect
What is a circuit diagram?
It is a symbolic representation of an electric circuit.
Which property of a conducting wire is utilised in making electric fuse?
Low melting point of the wire.
What happens if the filament of the bulb is broken?
The circuit would be incomplete and the bulb does not glow even if the switch is in the ‘ON’ position.
What is the use of a cell holder?
A cell holder is used to make battery of two or more cells.
How are the cells placed in the cell holder?
The cells are placed in the cell holder such that the positive terminal of one cell is connected to the negative terminal of the next cell.
Give two examples of the heating effect of current.
(i) Electric kettle
(ii) Hair dryers
Why should we buy electric appliances with the ISI mark?
The ISI mark ensures that the appliance is safe and wastage of energy is minimum. So we should buy only electric appliances with the ISI mark.
Name the device used to protect damages to the circuit due to excessive flow of current.
Electrical fuse or MCB.
What happens if by accident the current exceeds the safe limit?
The wires may become overheated and may cause fire.
What is a fuse?
A fuse is a safety device which prevents damages to electrical circuits and possible fires.
Who was the first person to notice the deflection of compass needle every time the current was passed through the wire?
Hans Christian Oersted.
What do the doctors use to take out small pieces of magnetic material accidently fallen in the eye?
Doctors use tiny electromagnets for this purpose.
Give one reason for short circuit.
Direct touching of wires with each other.
Why is an electric fuse required in all electrical appliances?
It is required to check excessive flow of electric current and save electrical appliances from further damage.
Why is it advisable not to touch a lighted electric bulb connected to the mains.
Lighted electric bulb connected to the mains may be very hot and can burn our hand badly.
Electric Current and Its Effects Class 7 Extra Questions Short Answer Type
Define a battery. Explain the arrangement of cells in a battery.
A battery is a combination of two or more cells in which cells are placed such that the positive terminal of one cell is connected to the negative terminal of the next cell. Many devices like torches, transistors, toys, TV remote controls, etc., use batteries. The cells are sometimes placed one after the other and sometimes side by side.
When does the current flow throughout the circuit? Explain.
When the switch is in the ‘ON’ position, and the positive terminal of the battery is connected to the negative terminal of the battery through wires then the circuit is said to be closed and the electric current flows throughout the circuit.
How many types of circuit are there? Describe.
There are two types of circuit
- closed circuit and
- open circuit.
(i) Closed-circuit: When the switch is in the ‘ON’ position and the circuit from the positive terminal of the battery to the negative terminal is complete then the circuit is said to be closed and the current flows throughout the circuit. Also the bulb glows in the closed circuit.
(ii) Open circuit: When the switch is in the ‘OFF’ position or the filament of the bulb is broken, the circuit is incomplete and it is said to be an open circuit. No current flows through any part of the circuit.
Why are wires of different materials and different lengths and thicknesses used?
The amount of heat produced in a wire depends on its material, length and thickness. Thus for different requirements, the wires of different lengths and thickness and materials are used.
What type of wire is used for making electric fuses?
Wires made of some special materials that melt quickly and break when large electric currents are passed through them are used for making electric fuses. For example, alloy of lead and tin.
What is an electromagnet?
A coil that behaves like a magnet when electric current is passed through it and loses its magnetism when the supply of electricity is broken is called an electromagnet. It is a temporary magnet made by coiling wire around an iron core; when current flows in the coil the iron behaves as a magnet. Electromagnets can be made very strong and can lift heavy loads.
Electric Current and Its Effects Class 7 Extra Questions Long Answer Type
Explain the working of an electric bell with diagram.
It consists of a coil of wire wound on an iron piece. The coil acts as an electromagnet. An iron strip with a hammer at one end is kept close to the electromagnet. There is a contact screw near the iron strip.
When the iron strip is in contact with the screw, the current flows through the coil which becomes an electromagnet. It, then, pulls the iron strip. In the process, the hammer at the end of the strip strikes the gong of the bell to produce a sound. However, when the electromagnet pulls the iron strip, it also breaks the circuit.
The current through the coil stops flowing and the coil is no longer behaves as an electromagnet. It no longer attracts the iron strip. The iron strip comes back to its original position and touches the contact screw again.
This completes the circuit. The current flows in the coil and the hammer strikes the gong again. This process is repeated in quick succession. The hammer strikes the gong every time the circuit is completed. This is how the bell rings.
When does an electric short circuit occur? What harm can it do?
When the plastic covering of both live wire and neutral wire removes due to wear and tear, these two wires come in contact with each other. Since, the resistance of neutral wire is very low, excessive current flow through the wire in a short time which heats the wire to a great extent. This can result in fires. Another reason of short circuiting is connection of many devices to a single socket. This can also lead to excessive flow of current.
What do you mean by overloading of an electric circuit? State two measures to avoid overloading.
The current flowing in domestic wiring at a particular time depends on the power ratings of the appliances which are being used. When a number of appliances are switched on at the same time, they take out an extremely large amount of current. This is called ‘overloading the circuit’. Now due to an extremely large amount of current flowing through them, the copper wires of household get heated to a very high degree and a fire may be started.
Two measures to avoid overloading are following:
- Too many appliances should not be connected to a single socket.
- Many electrical appliances of high power rating should not be run at the same time.
Explain construction of a simple electromagnet with a labelled diagram.
An electromagnet act on the principle of magnetic effect of the current. The coil of wire wound around an iron bar behaves like a magnet when electric current flows through it. When electric current is switched off, the coil generally loses its magnetism.
To construct an electromagnet, take a big iron nail or a big iron screw. Take a long piece of insulated copper wire and wind quite a few turns around the nail. Connect the ends of the wire to the terminals of a battery through a switch as shown in Fig. 14.19.
Place some pins on or near the end of the nail. Now switch on the current. You will observe that pins cling to the nail. Now switch off the current. You will observe that pins no longer get attracted to the nail.
Electric Current and Its Effects Class 7 Extra Questions HOTS
Why do birds do not get shock when they sit on high power live wire but we do?
As bird sit on only one wire, the circuit remains incomplete so they do not get shock.
Why are compact fluorescent lamps (CFLs) preferred over electric bulbs?
CFLs do not waste electricity as heat and thus consumes less energy whereas electric bulb along with light also give out heat.
Why are MCB preferred over electric fuses?
Due to following reasons MCB are preferred over electric fuses:
- MCB is more sensitive to overcurrent than fuse.
- Restoration of electric supply is quick. Restoration can be done by just switching the operating knob to its ‘ON’ position
- Handling MCB is electrically more safe than fuse.
Can we use same fuse in a geyser and a television set or any other electrical appliances? Explain.
No, different electrical appliances need different amount of current. A geyser generally takes more voltage of current in comparison to a television. Therefore the fuse in these will be of different ratings.
Why we must cover plug pin holes which are within the reach of children with cellotape or a plastic cover when not in use?
Children are usually not aware of electrocution and they can put their fingers or other conducting material into the plug pin holes. To protect them from electric shock we must cover plug pin holes with cellotape or plastic cover.
Electric Current and Its Effects Class 7 Extra Questions Value Based (VBQs)
Rama saw her mother running microwave oven, electric cooker and mixer grinder from a single socket. She immediately rushed to her mother and reminded her of overloading and its consequences. Rama’s mother immediately turned off the switch and connected them one by one according to her need. She felt very happy for Rama for her presence of mind.
(a) What is overloading?
(b) What are the consequences of overloading?
(c) What role do MCB plays in case of overloading?
(d) What value of Rama is shown here?
(a) When excessive amount of electric current passes through the wire, excessive heating take place, this is called overloading.
(b) Overloading can damage the circuit of house. It can also lead to fire.
(c) When there is overloading of current, MCB trips and switches off, which in turn cut off the supply of electricity and thus protect us from damages due to overloading of current.
(d) Rama is an intelligent, quick decision maker and helpful girl.
Class VII students thought to organise an campaign on ‘conserve energy’ in which they will include how to conserve electricity and what precautions one must take while handling electricity.
(a) Imagine that you are also participating in this campaign. What will you do to make it more effective and interesting?
(b) What precautions one must observe while working with the electricity.
(c) How can you conserve electricity?
(d) Do you think you also need to run an awareness campaign on certain problem or crisis related to your area. Why?
(a) We can make it more effective and interesting by organising play and some cultural programmes.
(b) Following precautions must be observed while working with the electricity:
- Do not touch switches with wet hand.
- All appliances must be properly earthed.
- Wear rubber shoes and gloves before coming in contact with electrical wire during repair or replacement.
- Do not conduct experiment with main supply.
(c) Use CFL bulb or tubelights.
- Switch off lights, fans, TV, etc., when not needed.
- Always run AC in auto mode
- Install efficient electrical appliances which consume less current.
(d) Do it yourself.