Reflection — Set 2
Physics · परावर्तन · Questions 11–20 of 70
An object is 30 cm in front of a plane mirror. The distance between the object and its image is?
Correct Answer: A. 60 cm
A plane mirror forms the image as far behind the mirror as the object is in front. So the image is 30 cm behind the mirror when the object is 30 cm in front. The separation between object and image is 30 + 30 = 60 cm.
If the angle of incidence is 35°, the angle between the incident ray and reflected ray is?
Correct Answer: B. 70°
In reflection, angle of incidence equals angle of reflection. Therefore the incident and reflected rays make equal angles with the normal. The angle between them is 35° + 35° = 70°.
A real image formed by a mirror is always?
Correct Answer: B. Inverted
A real image by a mirror forms where reflected rays actually meet. Such convergence produces an inverted image for mirrors that can form real images. A real image can generally be obtained on a screen.
In a spherical mirror, the principal focus lies on the?
Correct Answer: C. Principal axis
The principal focus is defined for rays parallel to the principal axis. After reflection from a spherical mirror, these rays meet or appear to meet at a point on the axis. Hence the focus lies on the principal axis.
A smooth and polished surface produces mainly?
Correct Answer: C. Regular (specular) reflection
On a smooth surface, the normals at nearby points are nearly parallel. So reflected rays remain orderly and form a clear image. This is called regular or specular reflection.
The unit commonly used for sound intensity level is?
Correct Answer: C. Decibel (dB)
Sound intensity level is a logarithmic measure of sound intensity. It is expressed in decibel (dB). A change of 10 dB corresponds to a tenfold change in intensity.
A person hears an echo 0.4 s after shouting. If speed of sound is 340 m/s, the distance to the reflecting wall is approximately?
Correct Answer: A. 68 m
For an echo, sound travels to the wall and back, so distance d = v × t / 2. Here d = 340 × 0.4 / 2 = 68 m. Echo calculations use round-trip time because the wave returns to the listener.
During reflection of light from a mirror, which quantity remains unchanged?
Correct Answer: C. Frequency of light
Reflection changes the direction of the light ray but not its frequency. In the same medium, the speed and frequency remain the same for the reflected wave. This is why the color of light does not change on reflection.
The point on a spherical mirror where the principal axis meets the mirror surface is called the?
Correct Answer: D. Pole
The pole is the geometric center point of the mirror surface. The principal axis is drawn through the pole and the center of curvature. Many distances for mirrors are measured from the pole.
The angle between the incident ray and the normal to the surface at the point of incidence is called?
Correct Answer: D. Angle of incidence
The angle of incidence is defined using the normal at the point where the ray strikes the surface. It measures how slanted the incident ray is from the perpendicular direction. This angle is used directly in the law of reflection.