Here in this post we provided NCERT Exemplar Problem Class 7 Science Electric Current and Its Effects Chapter 14 Full Explanation by group of Science Experts. We have provided here each questions answer with reason behind the answer.
Hope it help you!
Electric Current and Its Effects Class 7 Exemplar full Explanation:
1) When an electric current through a copper wire AB as shown in figure 14.1, the wire
a) Deflects a magnetic needle placed near it.
b) Becomes red hot.
c) Gives electric shock.
d) Behaves like a fuse.
Answer:- a) Deflects a magnetic needle placed near it.
As shown in figure. 14.1 when an electric current passes through an copper wire AB then the wire Deflects a magnetic needle placed near it.
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.
Answer:- c) there is a minimum limit on the current which can safely flow in the electric circuits.
These is statement is correct among the above about the electric fuse. Other are wrong in the case of Electric fuse.
3) Three bulbs A,B,C are connected in a circuit as shown in figure 14.2. 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.
Answer:- c) all the bulbs A, B, and C will glow at the same time.
All the bulbs will glow on the same time when the will be ON .
4) When a switch is in OFF position.
a) Circuit starting from the positive terminal of the cell stops at the switch.
b) Circuit is open.
c) No current flows through it.
d) 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.
Answer:- b) all are correct.
When switch is in off position then all the statements given above are correct.
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.
Answer:- d) we should never turn the switch in ON position.
We about never turn the switch in On position this precautions we don’t need to take while using electric gadgets/ appliances/ circuit.
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Very Short Answer Questions
6) Which property of a conducting wire is utilised in making electric fuse
Answer:-The property of a conducting wire is low melting point which is utilised in electric fuse.
The electric fuse is made with low melting point, thus when an electric current with high voltage is passed through the wire the fuse should melts before crossing the maximum voltage. Thus these for the prevention from high voltage passing through a circuit. If accidentally current exceeds the safe limit the wire may catch fire, thus the proper fuse in circuit placed there, it will be break. Therefore a fuse is a safety device having a property of low melting point.
7) Name the device used these days in place of electric fuses in electrical circuits ?
Answer:- The device which is uses these days in place of electric fuses in electrical circuits are miniature circuit breakers (MCBs) . These are the switches which automatically turned off when the current in circuit passing over the limit. We can turn it on by hands and thus the circuit again completed.
(8) Fill in the blanks :
i) Our body is a _________ of electricity.
Answer:- our body is a conductor of electricity.
ii) an electric cell produces electricity from the ________ ____________ in it.
Answer:- an electric cell produces electricity from the chemicals stored in it.
iii) in an electric circuit a fuse is a ________ ___________ to prevent possible fire.
Answer:- in an electric circuit a fuse is a safety device to prevent possible fire.
iv) A combination of two or more cells is called a __________ .
Answer:- A combination of two or more cells is called a battery.
9) Unscramble the following words.
i) TBTAYER
ii) SFEU
iii) HTRCO
iv) HICWTS
Answer:-
I) BATTERY
II) FUSE
III) TORCH
IV) SWITCH
(10) Paheli does not have a night lamp on 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.
Answer:- No. Paheli can not use the towel to cover the light. The towel may burn due to the heat produced in the light when it is on. These is due to heating effect of electric current. Putting towel on bulb will also be the wastage of electricity.
11) Why are compact fluorescent lamps (CFLs) preferred over electric bulbs ?
Answer:- compact fluorescent lamps CFLs are the better way for the electricity use. It is a efficient lighting source used rather than incandescent electric bulbs. Electric bulbs use more energy than the CFLs also high consumption of electricity . Therefore it is preferred to use over it.
12) Why is an electric fuse required in all electrical appliances?
Answer:- Fuses are made up with an special material which melts easily and break when high electric current is passed through it. When an high voltage current that means higher than the threshold voltage passes through the circuit then the wire of electric fuses break down by melting.
Fuses are necessary in all electrical appliances for the prevention from damaging to application by catching fire due to over heating, and to check the excessive flow of current. The heating effect of electric current may cause damage the application which can be prevented by electric fuse.
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Short Answer Questions
13) Can we use the same fuse in a geyser and a television set? Explain.
Answer:-
No . We cannot use the same fuse in a geyser and a television set. As the geyser and television set requires different amount of electric current to complete circuit. Thus different type of electric fuse should be used over there.
14) Name two electric devices for each where
i) heating effect of current is used and geyser.
Answer:- Room heater and geyser.
ii) magnetic effect of current is used.
Answer:- cranes to lift heavy load of magnetic material and Electric bell.
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?
Answer:- It is more necessary for the prevention of children. Children are Anabel to understand that putting fingers in the socket may get them electric shock due to flowing current in circuit. For the prevention the holes of plug may cover with cellotape.
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 electro magnet will attract more pins? Give reason.
Answer:- When an electric current is passed through a wire , that acts like a magnet . That is the magnetic effect of electric current. Like these electric current can be used to make magnets . When an wire winded over a iron nail tightly and when an electric current flows through it, it behaves like an magnet. This is called as ELECTROMAGNET.
Boojho and paheli both made electromagnet of 5/ turns of wire and 100 turns of wire respectively over an iron screw.
In that case paheli’s electromagnet which is winded with 100 turns of wire will attract more pins than boojho’s electromagnet, because it has more turns of wire, and therefore it is a strong electromagnet than boojho.
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Long Answer Questions
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 14.3. 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.
Answer:-
A) why does the pins are attracted to the nail?
B) What will happen if we connect more cells in the that circuit?
C) What will happen if we round the wire on the nail more tightly?
D) Will there be same attraction in More rounds of wire and less rounds of wire on the nails?
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 14.4 The current flowing in both the circuits is the same.
I) Will the heat produced on both the cases be equal? Explain.
Answer:- No. The heat produced in both cases is not equal. Because length of wire is not same. The amount of heat produced will be directly dependent upon the length of wire. As paheli’s wire is 10 cm and longer than boojho’s wire which is 5 cm therefore the amount of heat in paheli’s circuit will be more than boojho’s circuit.
II) Will the heat produced be the same if the wires taken by them are of equal lengths but of different thickness? Explain.
Answer:- No. If the thickness of wire is different then amount of heat will also be different. Heat produced is dependent upon the length of wire as well as the thickness of wire. Therefore if thickness is different amount of heat produced will also be different.
19) How does the magnetic effect of electric current help in the working of an electric bell ? Explain with the help of a diagram.
Answer:- Working of Electric bell
Electric bell is a type of ELECTROMAGNET in it.
Electric bell contains a coil of wounded wire on iron piece. Thus the coil act like an electromagnet when an current flows through it. In an electric bell a iron strip with an hammer like hard metalpiece is placed at one end close to electromagnet, and a contact screw near the iron strip.
When there is contact occur between the iron strip and screw the current flows in that coil and the coil becomes electromagnet. As soon as it becomes electromagnet it pulls the iron strip , and hammer on the side of strip gong the bell. On the gong a sound is produced.
Whenever the electromagnet pulls the strip and sound it produced the it also break circuit. Then the strip of iron comes on it original position and comes in contact with screw which again completes the circuit. When the current flows in coil again it gongs the bell after Strick of hammer . Thus this is how the electric bell works.
20) Draw the symbols of the following circuit components.
I) Electric cell
II) Switch in off position
III) Electric bulb
IV) Battery
Answer:-
1) Electric cell
Symbol of electric cell is –
2) Switch in off position
Symbol of switch in of position-
3) Electric bulb
Symbol of electric bulb-
4) Battery
Symbol of battery-