CBSE Class 10 Physics Light Reflection and Refraction MCQs Set 11

Answer: (b) 55°, 55°

Explanation:
1. The angle between the incident ray and the mirror surface is 35°, and the normal makes 90° with the surface.
2. Angle of incidence = 90° − 35° = 55°.
3. By the law of reflection, the angle of reflection is also 55°.

Teacher's Note:
1. Angles of incidence and reflection are always measured from the normal, never from the mirror surface.
2. If a ray makes θ with the surface, then i = 90° − θ.

Answer: (b) 1 m

Explanation:
1. A plane mirror forms the image as far behind the mirror as the object is in front of it.
2. Image distance = 0.5 m behind the mirror.
3. Distance between object and image = 0.5 m + 0.5 m = 1 m.

Teacher's Note:
1. Object-to-image distance in a plane mirror is twice the object distance.
2. Do not stop at 0.5 m; the image is behind the mirror.

Answer: (a) 3

Explanation:
1. Number of images = (360°/θ) − 1 when 360°/θ is an even integer.
2. Here (360°/90°) − 1 = 4 − 1 = 3.

Teacher's Note:
1. Learn the formula n = (360°/θ) − 1.
2. Two mirrors at right angles always give 3 images.

Answer: (c) all spherical mirrors

Explanation:
1. For a spherical mirror of small aperture, the principal focus lies midway between the pole and the centre of curvature.
2. So f = R/2 for both concave and convex mirrors.
3. It is not valid for lenses.

Teacher's Note:
1. R = 2f is a property of spherical mirrors of small aperture.
2. Do not apply it to lenses.

Answer: (c) size of the object is smaller than that of image

Explanation:
1. Magnification m = (height of image)/(height of object).
2. If m > 1 then image height is greater than object height.
3. So the object is smaller than its image.

Teacher's Note:
1. m > 1 means enlarged, m < 1 means diminished, m = 1 means same size.
2. The sign of m tells whether the image is real or virtual, not its size.

Answer: (b) is always virtual

Explanation:
1. Rays reflected from a convex mirror always diverge.
2. They only appear to meet when produced backwards, behind the mirror.
3. So the image is always virtual, erect and diminished.

Teacher's Note:
1. A convex mirror has no position of the object for which the image is real.
2. It is therefore used as a rear-view mirror.

Answer: (b) negative

Explanation:
1. An inverted image has its height measured below the principal axis, so it is taken as negative.
2. Hence m = h′/h is negative.

Teacher's Note:
1. Real images are inverted and have negative m.
2. Virtual images are erect and have positive m.

Answer: (a) 3.0 ft

Explanation:
1. To see the full image, the mirror must be at least half the height of the person.
2. Half of 6.0 ft = 3.0 ft.

Teacher's Note:
1. The minimum mirror length is half of one's height, whatever the distance from the mirror.
2. The ray diagram uses two similar triangles to prove this.

Answer: (c) located at the center of curvature of the mirror.

Explanation:
1. For an object at C the mirror formula gives v = u.
2. The image is real, inverted and of the same size, formed at C itself.

Teacher's Note:
1. Object at C gives image at C, the only position with m = −1.
2. This is used to find the radius of curvature in the laboratory.

Answer: (b) Second

Explanation:
1. Part of the light is reflected from the front glass surface, giving a faint first image.
2. Most of the light is reflected from the silvered back surface, giving the second image.
3. So the second image is the brightest.

Teacher's Note:
1. A thick mirror forms several images because of reflection from both glass surfaces.
2. The silvered surface reflects most light.

Answer: (c) a plane mirror

Explanation:
1. A plane mirror always forms a virtual, erect image equal in size to the object.
2. Concave and convex mirrors form virtual images of different sizes.

Teacher's Note:
1. Same size and virtual is the signature of a plane mirror.
2. Its magnification is +1.

Answer: (d) infinity

Explanation:
1. A plane mirror is a spherical mirror of infinite radius of curvature.
2. Since f = R/2, its focal length is infinite.
3. Parallel rays stay parallel after reflection, so they never meet.

Teacher's Note:
1. A plane mirror has R = ∞, f = ∞ and power zero.
2. Do not confuse infinite focal length with zero.

Answer: (d) All of these

Explanation:
1. For u = f, the reflected rays are parallel and meet only at infinity.
2. The image is real, inverted and highly enlarged, formed at infinity.
3. All three statements are correct.

Teacher's Note:
1. Object at F gives image at infinity.
2. This is why the bulb in a headlight is placed at the focus.

Answer: (d) real and point sized

Explanation:
1. Rays from an object at infinity are parallel to the principal axis.
2. After reflection they meet at the focus, forming a real, inverted and highly diminished, point-sized image.

Teacher's Note:
1. Object at ∞ gives image at F, real, inverted, point-sized.
2. Learn this together with 'object at F gives image at ∞'.

Answer: (c) convex mirror

Explanation:
1. A convex mirror gives a virtual, erect and diminished image for every position of the object.
2. A concave mirror gives a diminished image only if it is real, and a plane mirror gives an image of the same size.

Teacher's Note:
1. Diminished + virtual for all positions: convex mirror.
2. This property makes it useful as a rear-view mirror.

Answer: (b) a convex mirror

Explanation:
1. A convex mirror forms a diminished image of any object, so a tall distant building fits fully inside the mirror.
2. A plane mirror needs to be as large as half the image height, and a concave mirror gives a point-sized image of a distant object.

Teacher's Note:
1. Convex mirrors have a large field of view.
2. Think of a small convex traffic mirror showing a wide road.

Answer: (a) is less than one

Explanation:
1. A rear-view mirror is convex, and it always forms a diminished image.
2. So its magnification is positive but less than one.

Teacher's Note:
1. A convex mirror: 0 < m < 1 for every position of the object.
2. This is why vehicles seem farther than they are.

Answer: (d) virtual and erect

Explanation:
1. For an object between P and F of a concave mirror the reflected rays diverge.
2. They appear to meet behind the mirror, so the image is virtual.
3. Such an image is erect and enlarged.

Teacher's Note:
1. Behind the mirror means virtual.
2. Virtual images by single mirrors are always erect.

Answer: (d) all reflecting surfaces

Explanation:
1. The two laws of reflection (i = r, and incident ray, reflected ray and normal in one plane) hold at every point of every reflecting surface.
2. For curved mirrors the normal is the line joining the point to the centre of curvature.

Teacher's Note:
1. Laws of reflection are universal.
2. Do not limit them to plane mirrors.

Answer: (a) aperture

Explanation:
1. The width (diameter) of the reflecting surface of a spherical mirror is its aperture.
2. Radius of curvature is the radius of the sphere of which the mirror is a part, and focal length is the distance from the pole to the focus.

Teacher's Note:
1. Aperture = diameter of the mirror's reflecting surface.
2. Spherical mirrors of small aperture obey R = 2f.

Answer: (b) The height of the image should be taken as positive for both virtual and real image.

Explanation:
1. Heights above the principal axis are positive and heights below it are negative.
2. A virtual image is erect (above the axis, positive), but a real image is inverted (below the axis, negative).
3. So statement (b) is wrong.

Teacher's Note:
1. Sign of the image height depends on whether the image is erect or inverted.
2. Real image: negative height and negative magnification.

Answer: (c) When object is placed between the focus and centre of curvature

Explanation:
1. Object between F and C gives a real, inverted image beyond C, larger than the object.
2. At C the image is equal in size, and beyond C it is smaller.
3. Within F the image is virtual, not real.

Teacher's Note:
1. Real + larger: object between F and C.
2. Learn the concave mirror table.

Answer: (c) Between focus and pole

Explanation:
1. A positive magnification means a virtual, erect image.
2. A concave mirror forms such an enlarged image only when the object is between the focus and pole.

Teacher's Note:
1. Positive m with a concave mirror: object between P and F.
2. Beyond F the magnification is negative.

Answer: (c) Mirror A is concave and mirror B is plane

Explanation:
1. The image size stays equal to the object in a plane mirror, so B is plane.
2. In a concave mirror the erect image grows larger as the object approaches the focus, so A is concave.

Teacher's Note:
1. Plane mirror: constant size. Concave mirror: size increases as the object nears F.
2. A convex mirror's image does not grow so dramatically.

Answer: (c) At C

Explanation:
1. At C the image is formed at C, real, inverted and equal to the object in size.

Teacher's Note:
1. m = −1 only when the object is at C.
2. At F the image is at infinity; beyond C it is smaller.

Answer: (a) 0°

Explanation:
1. By the law of reflection, the angle of incidence is equal to the angle of reflection.
2. If the angle of reflection is 0°, the angle of incidence is 0°.

Teacher's Note:
1. i = r always.
2. A ray along the normal retraces its path.

Answer: (d) diminished and virtual

Explanation:
1. A convex mirror forms only virtual, erect and diminished images of a real object.
2. The image grows a little as the object approaches the pole, but it always remains diminished.

Teacher's Note:
1. Convex mirror image never becomes real or larger than the object.
2. Its size increases to equal the object only at the pole.

Answer: (c) real, inverted and enlarged

Explanation:
1. For an object between F and C the reflected rays converge beyond C.
2. The image is real, inverted and enlarged.

Teacher's Note:
1. Between F and C: real, inverted, enlarged, beyond C.
2. Write the table in your notebook.

Answer: (b) very near to the focus of the reflector

Explanation:
1. A concave reflector gives a powerful, nearly parallel beam when the source is at its focus.
2. So the bulb is kept very near the focus.

Teacher's Note:
1. Source at F gives a parallel beam after reflection.
2. Source at C would give a convergent beam.

Answer: (b) be parallel to the principal axis

Explanation:
1. By the reversibility of light paths, a ray passing through F of a concave mirror is reflected parallel to the principal axis.

Teacher's Note:
1. A ray parallel to the axis passes through F after reflection, and vice versa.
2. A ray through C retraces its path.

Answer: (d) Infinity

Explanation:
1. Each image acts as an object for the other mirror, so reflections continue repeatedly.
2. The number of images is infinite (though they become fainter).

Teacher's Note:
1. n = 360°/θ − 1 gives infinity for θ = 0°.
2. Parallel mirrors give an unlimited chain of images.

Answer: (c) It is diminished

Explanation:
1. The image in a plane mirror is erect, virtual, laterally inverted and the same size as the object, at the same distance behind the mirror.
2. It is not diminished.

Teacher's Note:
1. Plane mirror: m = +1, so the size never changes.
2. It is erect, virtual and laterally inverted.

Answer: (d) Beyond the centre of curvature

Explanation:
1. A negative magnification means a real image.
2. The magnitude 0.6 is less than 1, so the image is diminished, which happens only when the object is beyond C.

Teacher's Note:
1. m = −1 at C; magnitude less than 1 beyond C; magnitude greater than 1 between F and C.
2. Use the magnitude to place the object.

Answer: (b) Only (II)

Explanation:
1. A concave mirror reflects the parallel rays of the sun and makes them converge at its focus.
2. The food is kept at that point and it gets heated.
3. Only statement (II) is correct.

Teacher's Note:
1. Concave mirrors are converging mirrors.
2. They are used in solar cookers and solar furnaces.

Answer: (b) Concave in nature

Explanation:
1. A rear-view mirror is a convex mirror.
2. It gives a virtual, erect and diminished image with a wide field of view.
3. So 'concave in nature' is not a characteristic.

Teacher's Note:
1. Rear-view mirror: convex, wide view, virtual image.
2. Concave mirrors are used for shaving, not driving.

Answer: (a) Only A

Explanation:
1. A concave mirror forms the image of a distant object at its focus.
2. The focal length is the distance from the mirror to the screen, which is what student A measured.

Teacher's Note:
1. The building's distance does not matter, because it is effectively at infinity.
2. Measure from the mirror's pole to the screen.

Answer: (b) erect and diminished

Explanation:
1. A convex mirror always forms a virtual, erect and diminished image of a real object.

Teacher's Note:
1. Convex mirror: erect and diminished.
2. Move the pencil away and the image gets even smaller.

Answer: (d) either plane or convex

Explanation:
1. A plane mirror and a convex mirror always form erect images.
2. A concave mirror forms an erect image only when the object is within its focal length, and an inverted one when farther away.

Teacher's Note:
1. Always erect: plane or convex.
2. Concave gives inverted images beyond F.

Answer: (d) All of these

Explanation:
1. A convex mirror forms a virtual, erect and diminished image behind the mirror for every object position.
2. So all three statements are true.

Teacher's Note:
1. Object position does not change the nature of the image in a convex mirror.
2. Only the size and distance change.

Answer: (d) Image formed by a convex mirror is always virtual and erect.

Explanation:
1. The sign of magnification depends on whether the image is erect or inverted, not on its size.
2. A convex mirror always forms virtual and erect images, so m is positive.

Teacher's Note:
1. Positive m means erect.
2. Smaller size gives the value of m, not its sign.