NCERT Solutions for Class 7 Science Chapter 14 Electric Current And Its Effects are provided here with simple step-by-step explanations. These solutions for Electric Current And Its Effects are extremely popular among Class 7 students for Science Electric Current And Its Effects Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the NCERT Book of Class 7 Science Chapter 14 are provided here for you for free. You will also love the ad-free experience on Meritnation’s NCERT Solutions. All NCERT Solutions for class Class 7 Science are prepared by experts and are 100% accurate.
Page No 75:
Question 1:
When an electric current flows through a copper wire AB as shown in the given figure, the wire
(a) deflects a magnetic needle placed near it.
(b) becomes red hot.
(c) gives electric shock.
(d) behaves like a fuse.
Answer:
The current carrying wire produces magnetic field, due to which magnetic force will act on the magnetic needle placed near it.
Hence, the correct answer is option (a).
Page No 75:
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.
Answer:
Electric Fuse is designed to limit the maximum current through a circuit. There is a maximum limit of current above which the fuse blows due to the heating effect of current, and the circuit is broken.
Hence, the correct answer is option (c).
Page No 76:
Question 3:
Three bulbs A, B, C are connected in a circuit as shown in the given 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.
Answer:
All the bulbs A,B and C will glow simultaneously as soon as the switch is ‘ON’.
Hence, the correct answer is option (c).
Page No 76:
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
Answer:
If the switch is in OFF position, it means circuit is open, so no current will flow through the circuit at all.
Hence, the correct answer is option (b).
Page No 76:
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.
Answer:
It is required to turn on the electric circuit if needed while using electric gadgets/appliances/circuit.
Hence, the correct answer is option (d).
Page No 77:
Question 6:
Which property of a conducting wire is utilised in making electric fuse?
Answer:
Electric Fuse is designed to limit the maximum current through a circuit. The material used for fuse elements must be of low melting point. Because, if there is a current above desired limit, the fuse melts due to the heating effect of current, and the circuit is broken to stop current through the circuit. In this way the electric appliances attached to the circuit remains protected.
Page No 77:
Question 7:
Name the device used these days in place of electric fuses in electrical circuits.
Answer:
MCB (Miniature circuit breaker) is used these days in place of electric fuses in electrical circuits. It is relatively safer than the normal electric fuse.
Page No 77:
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 _________.
Answer:
(i) conductor
(ii) chemical
(iii) safety device
(iv) battery
Page No 77:
Question 9:
Unscramble the following words:
(i) TBTAYER
(ii) SFEU
(iii) HTRCO
(iv) HICWTS
Answer:
(i) Battery
(ii) Fuse
(iii) Torch
(iv) Switch
Page No 77:
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.
Answer:
No, Paheli has not taken the right step. As the period of time increases, the bulb will heat and heat will transfer from the surface of the bulb to the towel. Due to the excessive heating of towel, it may burn.
Page No 77:
Question 11:
Why are compact fluorescent lamps (CFLs) preferred over electric bulbs?
Answer:
Following are advantages of using CFLs:
CFLs reduce wastage of undesirable heat energy as in an ordinary bulb.
CFLs do not consume more energy than electric bulbs.
CFLs are more efficient than electric bulbs.
CFLs are less expensive in the long run because they last much longer than electric bulbs.
CFLs are environment-friendly as they have less carbon emission as compared to the bulb.
Page No 77:
Question 12:
Why is an electric fuse required in all electrical appliances?
Answer:
All electrical appliances are designed to work under certain current and voltage range. Excessive flow of current may damage the appliances or may catch fire. A fuse is a device which has low melting point. So when excessive current passes through it, due to the heating effect of electric current, it melts and breaks the circuit. The use of an electric fuse prevents the electric circuit and the appliance from possible damage by stopping the flow of high electric currents.
Page No 77:
Question 13:
Can we use the same fuse in a geyser and a television set? Explain.
Answer:
No, we cannot use the same fuse in geyser and television as the electricity required by both is different. A geyser (used to heat water) needs more electricity than a television. Therefore, the fuse used in these will be of different specifications ( melting point, maximum current limit as required).
Page No 78:
Question 14:
Name two electric devices for each where (i) heating effect of current is used and (ii) magnetic effect of current is used.
Answer:
Electric hair dryer, room heater and geyser works on heating effect of current.
Electric motor, electric bell and cranes to lift magnetic material works on magnetic effect of current.
Page No 78:
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?
Answer:
Kids may put their fingure into the socket of the pin holes within their reach and they may get an electric shock which could be dangerous. So, we must cover plug pinholes with cello tape or a plastic cover to prevent kids from getting electric shock.
Page No 78:
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 electro magnet will attract more pins? Give reason.
Answer:
The magnetic effect depends on the number of turns of wire on the electromagnet. The more the number of turns in winding, the stronger electromagnets will form. Therefore, Paheli’s electromagnet will attract more pins as it has more number of turns of wire on it and thus a stronger electromagnet.
Page No 78:
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 given 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.
Answer:
1. Why are the pins attracted towards the iron nail?
2. Are the pins be still attracted towards the iron nail, if free ends of the wire detached?
3. Is it possible to attract plane paper or plastic pins towards the iron nail in this activity?
Page No 78:
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 the given 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.
Answer:
(i) No, the amount of heat produced in both cases will not be equal. The amount of heat produced in a wire depends upon the length of the wire. If thickness (cross sectional area)and material of both wires be same, then the longer the length of the wire, the more its resistance and hence more heat will be produced on passing the current through it.
(ii) No, the amount of heat produced in both cases will not be equal again. The amount of heat produced in a wire also depends upon the thickness of the wire. If length and material of both wires be same, then the thicker the wire, the less its resistance and hence less heat will be produced on passing the current through it.
Page No 79:
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.
Answer:
When the switch is 'ON', the electric current starts passing through the wounded coil. The electromagnet becomes magnetised and generates a magnetic field that attracts the iron strip towards itself. The movement of the iron causes the hammer to hit the gong. In this way, the electric bell rings.
Page No 79:
Question 20:
Draw the symbols of the following circuit components.
(i) electric cell
(ii) switch in off position
(iii) electric bulb
(iv) battery
Answer:
ans
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