Electric Current and Its Effects: Class 7 Science Q&A
18 free answers on Electric Current and Its Effects (Science) for Class 7 students, across CBSE, ICSE and State boards. Includes questions such as “Can we use the same fuse in a geyser and a television set? Explain.”, “Why is an electric fuse required in all electrical appliances?”, “Why are compact fluorescent lamps (CFLs) preferred over electric bulbs?”
Question & Answer
Questions
- ScienceClass 7CBSE
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.
Soln: Paheli’s electromagnet will attract more pins as it has more number of turns of wire on it and thus a stronger electromagnet.
- ScienceClass 7CBSE
Why do we cover plug pinholes which are within reach of children with cello tape or a plastic cover when not in use?
Soln: Because the child may put his/her fingers into the socket, which results in electric shock, which may be fatal.
- ScienceClass 7CBSE
Name two electric devices for each, where (i) the heating effect of current is used and (ii) the magnetic effect of current is used.
Soln: Heating effect – Geyser, room heater. Magnetic effect – Electric bell, Cranes to lift magnetic material.
- ScienceClass 7CBSE
Can we use the same fuse in a geyser and a television set? Explain.
Soln: No, we cannot use the same fuse in a geyser and television because a geyser and a television set require a different amount of current. Therefore the fuse used in these will be of different ratings.
- ScienceClass 7CBSE
Why is an electric fuse required in all electrical appliances?
Soln: An electric fuse is required because it acts as a safety device and it checks excessive current flow.
- ScienceClass 7CBSE
Why are compact fluorescent lamps (CFLs) preferred over electric bulbs?
Soln: Compact fluorescent lamps (CFLs) are preferred over electric bulbs because CFLs consume less energy, and they will not waste energy in the form of heat.
- ScienceClass 7CBSE
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.
Soln: No, the steps taken by Paheli are wrong as the towel may get burned due to heat produced by the bulb and also, glowing the bulb unnecessarily will waste energy.
- ScienceClass 7CBSE
Unscramble the following words: (i) TBTAYER (ii) SFEU (iii) HTRCO (iv) HICWTS
Soln: Battery Fuse Torch Switch
- ScienceClass 7CBSE
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 _________.
Soln: (i) Our body is a conductor of electricity. (ii) An electric cell produces electricity from the Chemicals stored in it. (iii) In an electric circuit, a fuse is a Safety device to prevent a possible fire. (iv) A combination of two or more cells is called a battery.
- ScienceClass 7CBSE
Name the device used these days in place of electric fuses in electrical circuits.
Soln: Miniature Circuit Breaker (MCB).
- ScienceClass 7CBSE
Which property of a conducting wire is utilised in making an electric fuse?
Soln: The low melting point of the wire is utilized in making an electric fuse.
- ScienceClass 7CBSE
Which of the following precautions need not be taken while using electric gadgets/appliances/circuits? (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.
Soln: The answer is (d) We should never turn the switch in ON position. Explanation: To use electric gadgets/appliances/circuit switch should be turned on, hence statement d) is wrong.
- ScienceClass 7CBSE
When a switch is in OFF position, (i) circuit starting from the positive terminal of the cell stops at the switch. (ii) the circuit is open. (iii) no current flows through it. (iv) current flows after some time. Choose the combination of the 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
Soln: Answer is (b) (ii) and (iii) are correct Explanation: When the switch is off, the circuit will be incomplete hence it is open and no current flows through it.
- ScienceClass 7CBSE
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.
Soln: The answer is (c) There is a minimum limit on the current which can safely flow in the electric circuits. Explanation: In the case of an electric fuse, there is only a maximum limit on the current which can safely flow in the electric circuits.
- ScienceClass 7CBSE
An electrician is carrying out some repairs in your house. He wants to replace a fuse with a piece of wire. Would you agree? Give reasons for your response.
Solution: It is not a wise idea to replace the fuse with a piece of wire, as it has a very low melting point. In the case of the metal piece, the melting point will be high, and the circuit will be intact in case there is overload or overheating.
- ScienceClass 7CBSE
Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.
Solution: No, because plastic does not have the magnetic property to get attracted to a magnet; hence magnet cannot be used to separate plastic bags.
- ScienceClass 7CBSE
. Mark ‘T’ if the statement is true and ‘F’ if it is false: (a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (T/F) (b) When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T/F) (c) An electromagnet does not attract a piece of iron. (T/F) (d) An electric bell has an electromagnet. (T/F)
Solution: a) False b) True c) False d) True
- ScienceClass 7CBSE
Fill in the blanks: (a) Longer line in the symbol for a cell represents its ________ terminal. (b) The combination of two or more cells is called a _________. (c) When the current is switched ‘on’ in a room heater, it _______. (d) The safety device based on the heating effect of electric current is called a
Solution: (a) Longer line in the symbol for a cell represents its positive terminal. (b) The combination of two or more cells is called a battery. (c) When the current is switched ‘on’ in a room heater, it produces heat. (d) The safety device based on the heating effect of electric current is called a fuse.