Reflection — Set 1
Physics · परावर्तन · Questions 1–10 of 70
In a plane mirror, if an object is 20 cm in front of the mirror, the image forms at?
Correct Answer: A. 20 cm behind the mirror
A plane mirror forms an image at the same distance behind the mirror as the object is in front. So an object 20 cm in front gives an image 20 cm behind. This image is virtual and cannot be obtained on a screen.
Which statement expresses the second law of reflection?
Correct Answer: D. The incident ray, reflected ray, and the normal lie in the same plane
The second law of reflection states that the incident ray, reflected ray, and the normal are coplanar. This means they all lie in the same plane at the point of incidence. The first law separately relates the two angles with the normal.
A concave mirror has focal length 15 cm. Its radius of curvature is?
Correct Answer: C. 30 cm
For a spherical mirror, the radius of curvature is twice the focal length. So R = 2 × 15 cm = 30 cm. The center of curvature lies on the principal axis at this distance from the pole.
An echo is heard clearly when the reflected sound reaches the ear after at least about?
Correct Answer: A. 0.1 s
The ear distinguishes two sounds separately only if the time gap is about 0.1 s or more. A reflected sound arriving after this delay is heard as an echo. This usually needs the reflector to be sufficiently far away in air.
A convex mirror always forms an image that is?
Correct Answer: D. Virtual, erect, and diminished behind the mirror
A convex mirror causes reflected rays to diverge, so they appear to come from behind the mirror. Therefore the image is virtual and erect. It is also diminished, giving a wider field of view.
In a simple periscope, each plane mirror is typically set at an angle of?
Correct Answer: B. 45°
A plane mirror at 45° turns a light beam through 90° by reflection. A periscope uses two such mirrors to shift the line of sight. This arrangement allows viewing over obstacles.
A concave mirror has focal length 10 cm. Its power (in diopters) using the Cartesian sign convention is?
Correct Answer: D. -10 D
Power of a mirror is P = 1/f with f in meters using sign convention. For a concave mirror, f is negative, so P = 1/(-0.10) = -10 D. A negative sign indicates a converging mirror in this convention.
The left-right reversal seen in a plane mirror is called?
Correct Answer: D. Lateral inversion
In a plane mirror, the image appears reversed sideways compared to the object. This is called lateral inversion. It happens because the mirror swaps the front-back direction for the viewer.
Reflectance of a surface is defined as the ratio of?
Correct Answer: D. Reflected light energy to incident light energy
Reflectance tells what fraction of incident light is reflected by a surface. It is the ratio of reflected energy (or power) to incident energy (or power). Being a ratio, it has no unit.
For a ray incident normally on a plane mirror, the angle of reflection is?
Correct Answer: B. 0°
Angles in reflection are measured from the normal. At normal incidence, the incident ray makes 0° with the normal. So the reflected ray also makes 0° and retraces the same path.