Fill in the blanks
i) For a motor : a permanent magnet, then commercial motor : _
ii) Focal length of a lens; metre, then for power of a lens _____

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Solution

(1)Since permanent magnet cannot be large, hence electric magnets are used by the property of magnetic field created by moving charges.
(2)Since power is given by $P = \frac{1}{focal length of lens in m}$
Hence unit of power is $m^{- 1}$ or Diopter.

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Similar questions

Q. Fill in the blanks.
a) For a motor : a permanent magnet, then for a commercial motor : ..................
b) Focal length of a lens : metre, then for power of a lens : ..................

(a) What do you understand by the power of a lens? Name one factor on which the power of a lens depends.

(b) What is the unit of power of a lens? Define the unit of power of a lens.

(c) A combination of lenses for a camera contains two converging lenses of focal lengths 20 cm and 40 cm and a diverging lens of focal length 50 cm. Find the power and focal length of the combination.

Q. A lens of power

+ 2.0 D

is placed in contact with another of power

- 1.0 D

. The combination will behave like

Question 8
Which of the following statements is true?
(a) A convex lens has 4 dioptre power having a focal length 0.25 m.
(b) A convex lens has -4 dioptre power having a focal length -0.25 m.
(c) A concave lens has 4 dioptre power having a focal length 0.25 m.
(d) A concave lens has 4 dioptre power having a focal length -0.25 m.

Commercial electric motors do not use a permanent magnet to rotate the armature.

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Fill in the blanksi) For a motor : a permanent magnet, then commercial motor : _______ii) Focal length of a lens; metre, then for power of a lens ___________

(1)Since permanent magnet cannot be large, hence electric magnets are used by the property of magnetic field created by moving charges.(2)Since power is given by P=1focal length of lens in mHence unit of power is m−1 or Diopter.

Fill in the blanks
i) For a motor : a permanent magnet, then commercial motor : _
ii) Focal length of a lens; metre, then for power of a lens _____

(1)Since permanent magnet cannot be large, hence electric magnets are used by the property of magnetic field created by moving charges.
(2)Since power is given by $P = \frac{1}{focal length of lens in m}$
Hence unit of power is $m^{- 1}$ or Diopter.