If the speed of a moving magnet inside a coil increases, the electric current in the coil
- A.increases
- B.decreases
- C.reverses
- D.remains the same
Correct answer
Explanation
The correct answer is A, increases. When a magnet moves inside a coil, the magnetic flux linked with the coil changes, and this change produces an electromotive force and a current. This is electromagnetic induction, discovered by Michael Faraday in 1831. Faraday's law says the induced emf is equal to the rate of change of magnetic flux. If the magnet moves faster, the flux changes more quickly, so the induced emf is larger and, for the same coil resistance, the current is larger. A stronger magnet or a coil with more turns also raises the current. This is the principle behind electric generators and dynamos. Option B is wrong because a faster magnet gives a quicker change of flux, which never lowers the current. Option C is wrong because the direction depends on whether the magnet moves in or out and on which pole leads, as Lenz's law states, not on its speed. Option D is wrong because the current depends on the rate of change of flux, so it does not stay the same. Exam tip: induced current grows with speed of motion, magnet strength and number of turns.
Practice Questions
View allWhich one of the following is the special type of milk produced by a lactating mother, essential for the development of immune response of newborn baby in human?
- A.Breast milk produced after a month of childbirth
- B.Transitional milk
- C.Colostrum
- D.Mineralized milk
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Colostrum is the thick, yellowish first milk a mother produces in the first few days after childbirth.
Read the full explanation →Chemical formula of cooking soda is
- A.NaCl
- B.NaOCl
- C.Na2CO3
- D.NaHCO3
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Cooking soda, also called baking soda, is sodium hydrogen carbonate, also known as sodium bicarbonate. It is a mild base made from one sodium, one hydrogen, one carbon and three oxygen atoms.
Read the full explanation →Which one of the following statements regarding a thermos flask is NOT correct ?
- A.The walls of flask are separated by vacuum and made of glass which is a poor conductor of heat
- B.The glass walls themselves have shiny surfaces
- C.The surface of inner wall radiates good amount of heat and the surface of outer wall absorbs some of the heat that is radiated from the inner wall
- D.The cork supports are poor conductors of heat
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The statement is wrong because the inner wall of a thermos flask is silvered so that it radiates very little heat; the shiny outer surface also reflects heat back rather than absorbing it.
Read the full explanation →Work is said to be one Joule when a force of
- A.4 N moves an object by 25 cm.
- B.2 N moves an object by 1 m.
- C.1 N moves an object by 1 cm.
- D.1 N moves an object by 50 cm.
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Work equals force multiplied by displacement, and 4 N multiplied by 0.25 m gives exactly 1 joule.
Read the full explanation →Bacterial DNA is referred to as naked because it is not associated with :
- A.any scaffold
- B.proteins
- C.ribozymes
- D.plasmid
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In bacteria the DNA is not wrapped around histone proteins as it is in the chromosomes of eukaryotes, so it is called naked DNA.
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