A concave mirror is used to form an image of the sun on a white screen. If the lower half of the mirror is covered with a black paper, the effect on the image formed on the screen would be
If the lower half (or a part) of a mirror is covered with a black paper then a complete image of the object will be formed as before. However, the image will be less bright now.
Figure shows a ray of light as it travels from medium A to medium B. Refractive index of the medium B relative to medium A is
Here, ∠i = 60°, ∠r = 45°
Using Snell’s law of refraction, refractive index of medium B with respect to medium A.
A full length image of a distant tall building can definitely be seen by using
A full length image of a distant tall building can definitely be seen by using a convex mirror because a convex mirror always forms a virtual, erect and highly diminished image.
The angle of incidence of any light ray passing through the centre of curvature of a spherical mirror is
The angle of incidence of any light ray passing through the centre of curvature of a spherical mirror is 0°, because a line joining centre of curvature to any point on the mirror is a normal drawn at that point of the mirror.
A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is
Given h0 = +10 mm - + 0.1 cm
h2 = - 5 mm = -0 .5 cm
for real image, v = - 30 cm
∴ f = -20 cm
In case of a real and inverted image the magnification of a mirror is
Magnification is negative for a real and inverted image formed by a mirror.
The distance between the optical centre and point of convergence is called focal length in which of the following cases?
Parallel rays after refracting meet at the focus of a convex lens.
Rays from sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that size of the image is exactly equal to the size of the object ?
As light rays from sun (u = ∞) converge at a point 15 cm in front of a concave mirror, hence focal length of concave mirror f = - 15 cm.
To form an image of exactly same size as that of an object, the object should be placed at the centre of curvature (u = R = 2f) of mirror. Hence, the object should be placed at 30 cm in front of mirror.
A magnified real image is formed by a convex lens when the obiect is at
When object is at 2F, real inverted and same size image is formed by convex lens. So, according to question option (a) and (b) both are correct.
Image when object placed between F and 2F:-
Image when object is placed at 2F, which is of same size as that of object.
Image formed when object is at focus of the convex lens:-
When the object is placed at the first principal focus, the image is formed at infinity and the image is real, inverted and infinitely large.
A virtual, erect and magnified image of an object is to be produced with a concave mirror of focal length 12 cm. Object may be placed at a distance of
A concave mirror forms a virtual, erect and magnified image when an object is placed between pole and focus point of the mirror. As focal length of given concave mirror, hence object must be placed at a distance less than 12 cm i.e., u < 12 cm. Thus, the object may be placed at a distance of 10 cm from the mirror.