Reflection — Set 3
Physics · परावर्तन · Questions 21–30 of 70
In reflection, the angles are measured with respect to the?
Correct Answer: A. Normal
The normal is a line perpendicular to the reflecting surface at the point of incidence. The angle of incidence and angle of reflection are both measured from this normal. Measuring from the surface would give complementary angles instead.
A concave mirror has focal length 12 cm and an object is placed 24 cm in front of it. The image distance from the mirror is?
Correct Answer: B. 24 cm
Use the mirror formula 1/f = 1/v + 1/u with proper signs. With f = -12 cm and u = -24 cm, the calculation gives v = -24 cm. This means the real image forms 24 cm in front of the mirror at the center of curvature.
The magnification produced by a plane mirror is?
Correct Answer: A. +1
A plane mirror forms an image of the same size as the object. Therefore magnification is +1 because the image is erect. The plus sign indicates upright orientation.
For a concave mirror, when the object is at the center of curvature, the image forms?
Correct Answer: B. At the center of curvature, real, inverted, and same size
At the center of curvature, reflected rays meet back at the center of curvature. So the image is real and inverted and has the same size as the object. This is a standard ray-diagram result for concave mirrors.
The device that produces colorful patterns using repeated reflections is a?
Correct Answer: C. Kaleidoscope
A kaleidoscope uses multiple reflections between plane mirrors. This creates repeated images of small colored objects arranged symmetrically. Slight rotation changes the pattern because the reflections change.
A dentist uses a concave mirror mainly because it can produce a?
Correct Answer: C. Magnified upright image for close objects
When an object is within the focal length of a concave mirror, the image is virtual and magnified. This helps a dentist see fine details clearly. The image is also erect, making it easier to observe.
A plane mirror is rotated by 10°. The reflected ray rotates by?
Correct Answer: D. 20°
When a plane mirror rotates, the normal also rotates by the same angle. The angle of reflection changes by the same amount as the angle of incidence, so the ray turns twice. Therefore the reflected ray rotates by 2 × 10° = 20°.
In a convex mirror, the principal focus is?
Correct Answer: D. Behind the mirror and virtual
A convex mirror diverges parallel rays after reflection. These rays appear to come from a point behind the mirror. That point is the principal focus, and it is virtual.
Reverberation is the?
Correct Answer: A. Persistence of sound due to multiple reflections
Reverberation is the continued presence of sound in a room after the source stops. It occurs because sound reflects many times from walls and ceilings. Too much reverberation can make speech unclear.
Soundboards and curved reflectors in auditoriums are used mainly to?
Correct Answer: A. Reflect sound toward the audience evenly
Hard reflectors can direct sound energy toward listeners. Proper shapes spread reflected sound so more seats receive it. This improves loudness and clarity without changing the sound frequency.