Reflection — Set 5
Physics · परावर्तन · Questions 41–50 of 70
For a concave mirror, when the object is between the pole and the focus, the image is?
Correct Answer: D. Virtual, erect, and magnified
When the object is closer than the focal length, reflected rays diverge and appear to meet behind the mirror. This produces a virtual and erect image. The image is magnified, which is why such mirrors are used for close viewing.
The ability of a surface to reflect light effectively is commonly described by?
Correct Answer: D. Reflectivity
Reflectivity describes how well a surface reflects incident light. A higher reflectivity means a larger fraction of light is reflected. Polished metals generally have higher reflectivity than rough surfaces.
To reduce excessive reverberation in a room, it is most effective to use?
Correct Answer: A. Heavy curtains and acoustic panels
Reverberation decreases when more sound energy is absorbed rather than reflected. Soft and porous materials like curtains and acoustic panels absorb sound well. This improves speech clarity in halls and rooms.
A light ray makes 25° with the surface of a plane mirror. The angle of incidence is?
Correct Answer: D. 65°
Angles of incidence are measured from the normal, not from the mirror surface. The normal is perpendicular to the surface, so the two angles are complementary. Therefore i = 90° - 25° = 65°.
The working principle of a kaleidoscope is based on?
Correct Answer: A. Multiple reflection between plane mirrors
A kaleidoscope uses two or more plane mirrors kept at an angle. Light undergoes repeated reflections and forms many symmetric images. This produces repeated patterns from a few small objects.
A concave mirror is used as a shaving mirror because it gives a magnified image when the face is?
Correct Answer: C. Within the focal length
The correct answer is 'Within the focal length'. When the object is between the pole and focus of a concave mirror, the image is virtual and enlarged. This helps in seeing facial details clearly while shaving. The image remains erect, making it convenient for use.
A ray of light strikes a plane mirror with angle of incidence 40°. The angle between the mirror surface and the reflected ray is?
Correct Answer: D. 40° to the normal only
Angle of reflection equals angle of incidence, so the reflected ray makes 40° with the normal. The mirror surface is 90° to the normal, so the ray makes 90° - 40° = 50° with the surface. Complementary angles appear when measuring from the surface instead of the normal.
In reflection of light from a mirror, which property of the ray definitely changes?
Correct Answer: D. Direction of propagation
Reflection turns the light ray, so its direction changes. In the same medium, speed and frequency remain unchanged. This is why the color of light stays the same after reflection.
A plane mirror forms an image of height 3 cm when the object height is 3 cm. The magnification is?
Correct Answer: D. +1
A plane mirror forms an image equal in size to the object. So magnification m = image height / object height = 3/3 = +1. The positive sign shows the image is erect.
For a spherical mirror, the relation between focal length f and radius of curvature R is?
Correct Answer: A. f = R/2
A spherical mirror has its principal focus midway between the pole and the center of curvature. This gives the relation f = R/2. It is valid for both concave and convex mirrors in magnitude.