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NCERT Exemplar · Class 10 Science Light - Reflection and Refraction

38 questions · 38 still being checked

Multiple Choice Questions 1–10 (part 1 of 4)

  1. Exercise 1

    Which of the following can make a parallel beam of light when light from a point source is incident on it?
    (a)
    Concave mirror as well as convex lens
    (b)
    Convex mirror as well as concave lens
    (c)
    Two plane mirrors placed at 90\displaystyle 90° to each other
    (d)
    Concave mirror as well as concave lens

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    NCERT’s answer
    (a)
    (a) Concave mirror as well as convex lens — a point source at the principal focus gives a parallel emergent beam.\[\frac{1}{v}+\frac{1}{u}=\frac{1}{f},\ \ u=f\ \Rightarrow\ \frac{1}{v}=0\ \Rightarrow\ v=\infty \quad \text{(concave mirror)} \] \[\frac{1}{v}-\frac{1}{u}=\frac{1}{f},\ \ u=-f\ \Rightarrow\ \frac{1}{v}=0\ \Rightarrow\ v=\infty \quad \text{(convex lens)} \]

  2. Exercise 2

    A 10\displaystyle 10 mm long awl pin is placed vertically in front of a concave mirror. A 5\displaystyle 5 mm long image of the awl pin is formed at 30\displaystyle 30 cm in front of the mirror. The focal length of this mirror is
    (a)
    -30\displaystyle 30 cm
    (b)
    -20\displaystyle 20 cm
    (c)
    -40\displaystyle 40 cm
    (d)
    -60\displaystyle 60 cm

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    NCERT’s answer
    (b)
    (b) \(\displaystyle -20\,\mathrm{cm}\)Image is real and inverted: magnitude smaller than the object fixes the object beyond \(\displaystyle C\).\[m=\frac{h'}{h}=\frac{-5}{10}=-0.5=-\frac{v}{u} \] \[v=-30\,\mathrm{cm}\ \Rightarrow\ u=-60\,\mathrm{cm} \] \[\frac{1}{v}+\frac{1}{u}=\frac{1}{f} \] \[\frac{1}{-30}+\frac{1}{-60}=-\frac{1}{20}\ \mathrm{cm^{-1}}=\frac{1}{f} \] \[f=-20\,\mathrm{cm} \]

  3. Exercise 3

    Under which of the following conditions a concave mirror can form an image larger than the actual object?
    (a)
    When the object is kept at a distance equal to its radius of curvature
    (b)
    When object is kept at a distance less than its focal length
    (c)
    When object is placed between the focus and centre of curvature
    (d)
    When object is kept at a distance greater than its radius of curvature

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    (b), (c)Between pole and \(\displaystyle F\): image virtual, erect, magnified, behind the mirror. Between \(\displaystyle F\) and \(\displaystyle C\): image real, inverted, magnified, beyond \(\displaystyle C\). At \(\displaystyle C\) or beyond, the image is same size or smaller.

  4. Exercise 4

    Figure 10.1\displaystyle 10.1 shows a ray of light as it travels from medium A to medium B. Refractive index of the medium B relative to medium A is
    (a)
    3/2\displaystyle \sqrt{3} / \sqrt{2}
    (b)
    2/3\displaystyle \sqrt{2} / \sqrt{3}
    (c)
    1/2\displaystyle 1 / \sqrt{2}
    (d)
    2\displaystyle \sqrt{2}
    NCERT_Question_Class10_Science_Exemplar_Ch10_Q4

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    NCERT’s answer
    (a)
    (a) \(\displaystyle \sqrt3/\sqrt2\)From the figure, measured from the normal: \(\displaystyle i=60^\circ\) in A, \(\displaystyle r=45^\circ\) in B.\[n_{BA}=\frac{\sin i}{\sin r} \] \[n_{BA}=\frac{\sin 60^\circ}{\sin 45^\circ}=\frac{\sqrt3/2}{\sqrt2/2} \] \[n_{BA}=\frac{\sqrt3}{\sqrt2} \]

  5. Exercise 5

    A light ray enters from medium A to medium B as shown in Figure 10.2. The refractive index of medium B relative to A will be
    (a)
    greater than unity
    (b)
    less than unity
    (c)
    equal to unity
    (d)
    zero
    NCERT_Question_Class10_Science_Exemplar_Ch10_Q5

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    NCERT’s answer
    (a)
    (a) greater than unityThe ray bends toward the normal on entering B, so \(\displaystyle r<i\).\[r<i\ \Rightarrow\ \sin r<\sin i \] \[n_{BA}=\frac{\sin i}{\sin r}>1 \]

  6. Exercise 6

    Beams of light are incident through the holes A and B and emerge out of box through the holes C and D respectively as shown in the Figure 10.3. Which of the following could be inside the box?
    (a)
    A rectangular glass slab
    (b)
    A convex lens
    (c)
    A concave lens
    (d)
    A prism
    NCERT_Question_Class10_Science_Exemplar_Ch10_Q6

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    NCERT’s answer
    (a)
    (a) A rectangular glass slab — beams leave parallel to their incident direction but shifted sideways (C below A, D below B); a lens would converge or diverge them, a prism would deviate them.

  7. Exercise 7

    A beam of light is incident through the holes on side A and emerges out of the holes on the other face of the box as shown in the Figure 10.4. Which of the following could be inside the box?
    (a)
    Concave lens
    (b)
    Rectangular glass slab
    (c)
    Prism
    (d)
    Convex lens
    NCERT_Question_Class10_Science_Exemplar_Ch10_Q7

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    NCERT’s answer
    (d)
    (d) Convex lensAll ten parallel rays entering at A cross a single point near B and re-emerge in reversed vertical order — the signature of rays converging at a focus.

  8. Exercise 8

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

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    NCERT’s answer
    (a)
    (a) Convex lens: \(\displaystyle f\) is positive by sign convention. \[P=\frac{1}{f}=\frac{1}{+0.25\,\mathrm{m}} \] \[P=+4\,\mathrm{D} \] A converging lens must carry positive power, so only \(\displaystyle f=+0.25\,\mathrm{m}\) with \(\displaystyle P=+4\,\mathrm{D}\) is self-consistent.

  9. Exercise 9

    Magnification produced by a rear view mirror fitted in vehicles
    (a)
    is less than one
    (b)
    is more than one
    (c)
    is equal to one
    (d)
    can be more than or less than one depending upon the position of the object in front of it

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    NCERT’s answer
    (a)
    (a) A convex mirror diverges rays, forming a virtual, erect, diminished image at every object distance.Smaller-than-object images give the wide field of view needed behind a vehicle.

  10. Exercise 10

    Rays from Sun converge at a point 15\displaystyle 15 cm in front of a concave mirror. Where should an object be placed so that size of its image is equal to the size of the object?
    (a)
    15\displaystyle 15 cm in front of the mirror
    (b)
    30\displaystyle 30 cm in front of the mirror
    (c)
    between 15\displaystyle 15 cm and 30\displaystyle 30 cm in front of the mirror
    (d)
    more than 30\displaystyle 30 cm in front of the mirror

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    NCERT’s answer
    (b)
    (b) Sun's parallel rays meet at the focus: \[f=15\,\mathrm{cm} \] \[R=2f=30\,\mathrm{cm} \]An object at the centre of curvature \(\displaystyle C\) images back onto \(\displaystyle C\), same size, so it must stand $\displaystyle 30$ cm from the mirror.