An object is placed first at infinity and then at 20 cm from the object side focal plane of the convex lens. The two images thus formed are 5 cm apart. The focal length of the lens is
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(a) 5 cm |
(b) 10 cm |
(c) 15 cm |
(d) 20 cm |
(b) 10 cm
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.
Assertion : Coloured spectrum is seen when we look through a muslin cloth.
Reason : It is due to the diffraction of white light on passing through fine slits.
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(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
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(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
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(c) If assertion is true but reason is false. |
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(d) If the assertion and reason both are false. |
Angular width of central maxima in the Fraunhoffer diffraction pattern of a slit is measured. The slit is illuminated by light of wavelength 6000 Å. When the slit is illuminated by light of another wavelength, the angular width decreases by 30%. The wavelength of this light will be
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(a) 6000 Å |
(b) 4200 Å |
(c) 3000 Å |
(d) 1800 Å |
The ratio activity of an element becomes 1/64th of its original value in 60 sec. Then the half life period is
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(a) 5 sec |
(b) 10 sec |
(c) 20 sec |
(d) 30 sec |
Match List I with List II and select the correct answer using the codes given below the lists :
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List I (Position of the object) |
List II (Magnification) |
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(I) An object is placed at focus before a convex mirror |
(A) Magnification is -∞ |
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(II) An object is placed at centre of curvature before a concave mirror |
(B) Magnification is 0.5 |
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(III) An object is placed at focus before a concave mirror |
(C) Magnification is +1 |
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(IV) An object is placed at centre of curvature before a convex mirror |
(D) Magnification is -1 |
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(E) Magnification is 0.33 |
Codes :
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(a) I-B, II-D, III-A, IV-E |
(b) I-A, II-D, III-C, IV-B |
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(c) I-C, II-B, III-A, IV-E |
(d) I-B, II-E, III-D, IV-C |
