NCERT Exemplar Class 7 Science Chapter 14 Electric Current and Its Effects are part of NCERT Exemplar Class 7 Science. Here we have given NCERT Exemplar Class 7 Science Solutions Chapter 14 Electric Current and Its Effects.
NCERT Exemplar Class 7 Science Solutions Chapter 14 Electric Current and Its Effects
Multiple Choice Questions
Question 1.
When an electric current flows through a copper wire AB as shown in figure, the wire
(a) deflects a magnetic needle placed near it.
(b) becomes red hot.
(c) gives electric shock.
(d) behaves like a fuse.
Solution:
(a) A current carrying wire acts as a magnet with a magnetic field around it, the strength of which depends upon the amount of current passing through it.
Question 2.
Choose the statement which is not correct in the case of an electric fuse.
(a) Fuses are inserted in electric circuits of all buildings.
(b) There is a maximum limit on the current which can safely flow through the electric circuits.
(c) There is a minimum limit on the current which can safely flow in the electric circuits.
(d) If a proper fuse is inserted in a circuit it will blow off if current exceeds the safe limit.
Solution:
(c)
Question 3.
Three bulbs A, B, C are connected in a circuit as shown in figure. When the switch is ‘ON’
(a) bulb C will glow first.
(b) bulb B and C will glow simultaneously and bulb A will glow after some time.
(c) all the bulbs A, B and C will glow at the same time.
(d) the bulbs will glow in the order A, B and C.
Solution:
(c) As soon as the switch is ‘ON’, current can be found everywhere in the circuit.
Question 4.
When a switch is in OFF position,
(i) circuit starting from the positive terminal of the cell stops at the switch.
(ii) circuit is open.
(iii) no current flows through it.
(iv) current flows after some time.
Choose the combination of correct answer from the following.
(a) all are correct
(b) (ii) and (iii) are correct
(c) only (iv) is correct
(d) only (i) and (ii) are correct
Solution:
(b)
Question 5.
Which of the following precautions need not be taken while using electric gadgets/appliances/ circuit?
(a) We should never touch a lighted electric bulb connected to the mains.
(b) We should never experiment with the electric supply from the mains or a generator or an inverter.
(c) We should never use just any wire or strip of metal in place of a fuse.
(d) We should never turn the switch in ON position.
Solution:
(d)
Very Short Answer Type Questions
Question 6.
Which property of a conducting wire is utilised in making electric fuse?
Solution:
A conducting wire should have low melting point if it is utilised in making electric fuse.
Question 7.
Name the device used these days in place of electric fuses in electrical circuits.
Solution:
Miniature circuit breaker (MCB) is used these days in place of electric fuses in electrical circuits.
Question 8.
Fill in the blanks:
(i) Our body is a ________ of electricity.
(ii) An electric cell produces electricity from the ________ in it.
(iii) In an electric circuit a fuse is a ________ to prevent possible fire.
(iv) A combination of two or more cells is called a ________.
Solution:
(i) conductor
(ii) chemicals stored
(iii) safety device
(iv) battery
Question 9.
Unscramble the following words:
(i) TBTAYER
(ii) SFEU
(iii) HTRCO
(iv) HICWTS
Solution:
(i) BATTERY
(ii) FUSE
(iii) TORCH
(iv) SWITCH
Question 10.
Paheli does not have a night lamp in her room.
She covered the bulb of her room with a towel in the night to get dim light. Has she taken the right step? Give one reason to justify your answer.
Solution:
No, the towel may burn due to the heat produced by the bulb. Besides, it will also result in wastage of electric energy. She could have used a lampshade.
Question 11.
Why are compact fluorescent lamps (CFLs)
preferred over electric bulbs?
Solution:
CFLs do not waste electricity as heat unlike electric bulbs.
Question 12.
Why is an electric fuse required in all electrical appliances?
Solution:
An electric fuse is required in all electrical appliances because it is a safety device and checks the excessive flow of electric current.
Short Answer Type Questions
Question 13.
Can we use the same fuse in a geyser and a television set? Explain.
Solution:
No, a geyser and a television set require different amount of current to operate
Name two electric devices for each where (i) heating effect of current is used and (ii) magnetic effect of current is used.
Maim Heating effect – Geyser, room heater. Magnetic effect – Electric bell, Cranes to lift magnetic material.
Question 15.
Why do we cover plug pin holes which are within the reach of children with cellotape or a plastic cover when not in use?
Solution:
The child may put his/her fingers into the socket and he/she may get an electric shock which could be fatal. Plastic/cellotape are bad conductors of electricity and hence chances of electric shock gets reduced.
Question 16.
Boojho made an electromagnet by winding 50 turns of wire over an iron screw. Paheli also made an electromagnet by winding 100 turns over a similar iron screw. Which electromagnet will attract more pins? Give reason.
Solution: Paheli’s electromagnet will attract more pins as it has more number of turns of wire on it and thus a stronger electromagnet.
Long Answer Type Questions
Question 17.
Your teacher has shown you the following activity.
Activity: Teacher has wound a long insulated piece of wire around an iron nail in the form of a coil. Free ends of the wire are connected to a cell through a switch as shown in the figure. The current is switched on and some pins are placed near the ends of the nail.
Write down any three questions that come to your mind about this activity. Electric Current and its Effects
Solution:
Some of the questions can be
(i) Why does the nail attract the pins?
(ii) What will happen if we connect more cells in the circuit?
(iii) What will happen if we use some other material like a straw in place of the nail?
(iv) What will happen if we wrap the wire on the nail more tightly?
Question 18.
Paheli took a wire of length 10 cm. Boojho took a wire of 5 cm of the same material and thickness. Both of them connected the wires as shown in the circuit given in figure. The current flowing in both the circuits is the same.
(i) Will the heat produced in both the cases be equal? Explain.
(ii) Will the heat produced be the same if the wires taken by them are of equal lengths but of different thickness? Explain.
Solution:
(i) No, the amount of heat produced in both the cases will not be equal. Amount of heat produced in a wire depends upon the length of the wire.
(ii) No, the amount heat produced in the wire depends upon the thickness of the wire.
Question 19.
How does the magnetic effect of electric current help in the working of an electric bell? Explain with the help of a diagram.
Solution:
The door bell or the electric bell makes use of the principle of an electromagnet. A horseshoe type of electromagnet is used in an electric bell which is connected to the source of current through a switch. It has a metallic gong, a hammer to strike the gong, and screw attached to a soft iron strip.
When the button is pressed, the circuit is complete, and the hammer gets attracted to the gong thereby striking it to produce a ringing sound.
Question 20.
Draw the symbols of the following circuit components.
(i) electric cell
(ii) switch in off position
(iii) electric bulb
(iv) battery
Solution:
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