The focal length of a mirror is given by the mirror formula:

1/f = 1/v + 1/u

where:
f is the focal length,
v is the image distance, and
u is the object distance.

In a concave mirror, the object distance (u) is taken as negative and the image distance (v) is also taken as negative if the image is formed on the same side as the object.

Given in the problem:
u = -20 cm (object is 20 cm from the focus, on the same side)
v = -5 cm (image is 5 cm from the focus, on the same side)

Substituting these values into the mirror formula:

1/f = 1/(-5) + 1/(-20)
1/f = -0.2 - 0.05
1/f = -0.25

Therefore, the focal length f = -1/0.25 = -4 cm.

The negative sign indicates that the mirror is concave. So, the focal length of the mirror is 4 cm. None of the options provided are correct.

Question

The focal length of a mirror is given by the mirror formula:

1/f = 1/v + 1/u

where:
f is the focal length,
v is the image distance, and
u is the object distance.

In a concave mirror, the object distance (u) is taken as negative and the image distance (v) is also taken as negative if the image is formed on the same side as the object.

Given in the problem:
u = -20 cm (object is 20 cm from the focus, on the same side)
v = -5 cm (image is 5 cm from the focus, on the same side)

Substituting these values into the mirror formula:

1/f = 1/(-5) + 1/(-20)
1/f = -0.2 - 0.05
1/f = -0.25

Therefore, the focal length f = -1/0.25 = -4 cm.

The negative sign indicates that the mirror is concave. So, the focal length of the mirror is 4 cm. None of the options provided are correct.

Knowee AI · Accepted Answer

The focal length of a mirror is given by the mirror formula:

1/f = 1/v + 1/u

where:
f is the focal length,
v is the image distance, and
u is the object distance.

In a concave mirror, the object distance (u) is taken as negative and the image distance (v) is also taken as negative if the image is formed on the same side as the object.

Given in the problem:
u = -20 cm (object is 20 cm from the focus, on the same side)
v = -5 cm (image is 5 cm from the focus, on the same side)

Substituting these values into the mirror formula:

1/f = 1/(-5) + 1/(-20)
1/f = -0.2 - 0.05
1/f = -0.25

Therefore, the focal length f = -1/0.25 = -4 cm.

The negative sign indicates that the mirror is concave. So, the focal length of the mirror is 4 cm. None of the options provided are correct.

In a concave mirror, an object is placed at a distance of 20 cm from the focus and the image is formed at a distance of 5 cm from the focus. What will be the focal length of the mirror?5 cm10 cm20 cm30 cm

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