50 questions · timed · auto-graded
Explanation:
According to the sign convention, the focal length for both a concave mirror and a concave lens is negative.
Explanation:
Since it is opaque and does not let light to pass through it.
Explanation:
From the given figures we can conclude that the device X is a convex lens as it converges the rays and the device Y is a concave mirror as it also converges the rays but in the same side of the mirror .Their focal lengths are 20 cm and 25 cm respectively Regards.
Explanation:
The angle between the incident ray and the normal is known as the angle of incidence, and the angle between the emergent ray and the normal is known as the angle of emergence. The emergent ray is bent at an angle with the direction of the incident ray. This angle is called the angle of deviation.
Explanation:
Since the emergent ray is always parallel to the incident ray, therefore the angle of incidence is always equal to the angle of emergence i.e.,
$\angle\text{i}=\angle\text{e}\ .....\text{(i)}$
Also, when a light ray travels from rarer to denser medium, it bends towards the normal. Hence
$\angle\text{i}>\angle\text{r}\ ..... \text{(ii)}$
From (i) and (ii), we get
$\angle\text{i}=\angle\text{e}>\angle\text{r}$
Hence, the correct answer is $\angle\text{i}=\angle\text{e}>\angle\text{r}.$
Explanation:
The position of object is not known whether it is at infinity or beyond centre of curvature or at centre of curvature of lens. So depending upon the position of object we have to move the lens away or towards the screen.
Explanation:
or r < i
In refraction of light through a glass slab, the emergent ray is parallel to the incident ray. Thus, $\angle\text{i}=\angle\text{e}$.
Explanation:
The angle between the normal and the incident ray is the angle of incidence. The angle between the normal and the emergent ray is the angle of emergence. The correctly marked angles are shown in the diagram below:
Explanation:
The incident rays after passing through the lens converge at the focus. So, the device 'X' is a converging or a convex lens. The distance between the lens and the screen gives the focal length of the lens.
Explanation:
When a ray of light passes through a rectangular glass slab then due to change in the refractive index from air to glass and then glass to air, the light is refracted. The angle of incidence is equal to the angle of emergency of light ray and also greater than angle of refraction.
Explanation:
Ray 2, 3 and 4 are obeys the laws of refraction.
Ray 2 is parallel to the principal axis and passes through the principal focus after refraction.
Ray 3 passes from the optical centre of the lens and emerges without any deviation.
Ray 4 is passing through the principal focus and after refraction from a convex lens emerges parallel to the principal axis.
Ray 1 and 5 cannot pass through the focus after refraction as they are not parallel to the principal axis.
Ray 2, 3 and 4 are obeys the laws of refraction.
Ray 2 is parallel to the principal axis and passes through the principal focus after refraction.
Ray 3 passes from the optical centre of the lens and emerges without any deviation.
Ray 4 is passing through the principal focus and after refraction from a convex lens emerges parallel to the principal axis.
Ray 1 and 5 cannot pass through the focus after refraction as they are not parallel to the principal axis.
Explanation:
Light rays from infinity are converged at the focal point of the convex lens. Therefore, the focal length of the convex lens is 20cm.
Hence, the correct option is C.
Explanation:
Given, focal length of the image, f = 10cm.
Thus, the object is placed at 2F (2 × 10 = 20cm). Hence, the image is also formed at 2F.
The image will be of same size as that of the object and is real and inverted.
Explanation:
Since the emergent ray is always parallel to the incident ray, therefore the angle of incidence is always equal to the angle of emergence i.e.,
$\angle\text{i}=\angle\text{e}\ .....\text{(i)}$
Also, when a light ray travels from rarer to denser medium, it bends towards the normal. Hence
$\angle\text{i}>\angle\text{r}\ .....\text{(ii)}$
From (i) and (ii), we get
$\angle\text{i}=\angle\text{e}>\angle\text{r}$
Hence, the correct answer is $\angle\text{i}=\angle\text{e}>\angle\text{r}.$
Explanation:
The rays from a distant object (from infinity) always converge at the focus of the mirror. So the position of the screen in this case will give the location of the focus and the distance of screen from the pole of the mirror will give the focal length of the mirror. Also the image formed in such a case is real, inverted and diminished, so the correct answer is real, inverted and diminished.
Explanation:
In the case of candle flame, the object is placed beyond c, which means the image is formed or focused between c and f. in second case, the object or sun is at infinity, so the image will be formed at focus. This means that the distance between image and lens has decreased in the second case. Either we have to the screen towards the lens or the lens towards the screen.
So, option (a) is correct.
Explanation:
In refraction of light through a glass prism, there is deviation or change in the path of light passing through the prism.
Explanation:
Light rays from infinity are converged at the focal point of the convex lens. Therefore, the focal length of the convex lens is 20 cm.
Hence, the correct option is C.
Explanation:
Since the image is focused, the spherical mirror is a concave mirror. For second mirror the distance is increased to focus the image on the screen. Hence, focal length is more than that of first mirror.
Explanation:
To get the focal length of the mirror, the student should measure the distance between mirror and screen because when the object is at infinity, the image is formed at focus i.e. between screen and mirror. So, the distance between screen and mirror should be measured.
Explanation:
Since the emergent ray is always parallel to the incident ray, therefore the angle of incidence is always equal to the angle of emergence i.e.,
$\angle\text{i}=\angle\text{e}\ .....\text{(i)}$
Also, when a light ray travels from rarer to denser medium, it bends towards the normal. Hence
$\angle\text{i}>\angle\text{r}\ .....\text{(ii)}$
From (i) and (ii), we get
$\angle\text{i}=\angle\text{e}>\angle\text{r}$
Hence, the correct answer is $\angle\text{i}=\angle\text{e}>\angle\text{r}.$
| S. No. | $\angle\text{ i}$ | $\angle\text{ r}$ | $\angle\text{ e}$ |
| I | $30^{0}$ | $19^{0}$ | $29^{0}$ |
| II | $40^{0}$ | $28^{0}$ | $40^{0}$ |
| III | $50^{0}$ | $36^{0}$ | $50^{0}$ |
| IV | $60^{0}$ | $40^{0}$ | $59^{0}$ |
Explanation:
For best results, the following conditions must be satisfied:
Out of the 4 observations, the first observation, that is angle i = 30º; angle r = 19º and angle e = 29º is the correct observation. In this case, $\frac{\sin 30^\circ}{\sin 19^\circ}=1.535$.
Explanation:
Since the emergent ray is always parallel to the incident ray, therefore the angle of incidence is always equal to the angle of emergence i.e.
$\angle\text{i}=\angle\text{e}\ .....(\text{i})$
Also, when a light ray travels from rarer to denser medium, it bends towards the normal. Hence
$\angle\text{i}>\angle\text{r}\ .....(\text{ii})$
From (i) and (ii), we get
$\angle\text{i}=\angle\text{e}>\angle\text{r}$
Hence, the correct answer is $\angle\text{i}=\angle\text{e}>\angle\text{r}$
To find the focal length of a concave mirror, Sita should choose which one of the following set-ups?
Explanation:
If the refractive index of the medium (dispersing medium in our case "glass") through which the light passes during dispersion is greater than the medium through which the light enters (in our case "air") the dispersing medium, then the net deviation in the path of light is always towards the thicker part of the prism.
Explanation:
A ray comes from infinity, after refraction through a convex lens, meet at the second principal focus. So, screen should be placed at the second principal focus of a convex lens. e.g., screen should be placed at 15cm from the pole of convex lens.
Now, the position of the screen on the optical bench = distance between screen from the pole of convex lens + distance of optical bench from the pole of convex lens {as you can see in attachment}
= 15 cm + 42.7cm
= 57.7cm
Hence, option (C) is correct
Explanation:
Since the object and the image are on the same side, and the image is real (since it is focused on a screen) the device X is a concave mirror of focal length 20cm.
Explanation:
A ray comes from infinity, after refraction through a convex lens, meet at the second principal focus. So, screen should be placed at the second principal focus of a convex lens. e.g., screen should be placed at 15cm from the pole of convex lens.
Now, the position of the screen on the optical bench = distance between screen from the pole of convex lens + distance of optical bench from the pole of convex lens {as you can see in attachment}
= 15cm + 42.7cm
= 57.7cm
Hence, option (C) is correct.
