Can a wire that is generally used for fuse be used as the heating coil of geyser ?Justify.
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Answers
Explanation:
Nichrome is used for making heating element of electrical appliances. Because nichrome does not oxidize and burn easily at high temperature i.e.it has higher melting and boiling point than metals. Thus it does not melt even when a large amount of heat is produced due to passage of current. Moreover, It has higher resisistivity and consequently a higher resistance.Therefore, it will resist the flow of charges more, and lead to development of heat faster.
Explanation:
When an electric current flows through a copper wire AB as shown in figure, the wire
NCERT Exemplar Problems Class 7 Science – Electric Current and Its Effects-1
(a) deflects a magnetic needle placed near it
(b) becomes red hot
(c) gives electric shock
(d) behaves like a fuse
Answer:
(c) It deflects a magnetic needle placed near it because a magnetic field is created when the current passes 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.
Answer:
(c) In case of electric fuse, there is only a maximum limit on the current which can safely flow in the electric circuits.
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.
NCERT Exemplar Problems Class 7 Science – Electric Current and Its Effects-3
Answer:
(c) All the bulbs will glow simultaneously because there is no time lag in the flow of current as soon as the circuit is complete.
Question 4:
When a switch is in OFF position,
(i) circuit starting from positive terminal of the cell stops at the switch
(ii) circuit is open
(iii) no current flows through it
(iv) current flows after sometime
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) (i) and (ii) are correct
Answer:
(b) When the switch is in OFF position, circuit is incomplete. It is said to be open and therefore, no current flows through it.