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An object is placed at a distance of 30 cm from a convex lens of focal length 20 cm. Find the position of the image.

Question

An object is placed at a distance of 30 cm from a convex lens of focal length 20 cm. Find the position of the image.

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Solution 1

To find the position of the image formed by a convex lens, we can use the lens formula:

1/f = 1/v - 1/u

Where: f = focal length of the lens v = distance of the image from the lens u = distance of the object from the lens

Given: f = 20 cm u = -30 cm (negative sign indicates that the object is placed on the same side as the incident light)

Substituting the given values into the lens formula, we have:

1/20 = 1/v - 1/-30

Simplifying the equation, we get:

1/20 = 1/v + 1/30

To solve for v, we can find the common denominator:

1/20 = (3 + 2)/60

1/20 = 5/60

Now, we can equate the numerators:

1 = 5v/60

Cross-multiplying, we have:

60 = 5v

Dividing both sides by 5, we get:

v = 12 cm

Therefore, the position of the image formed by the convex lens is 12 cm from the lens.

This problem has been solved

Solution 2

Sure, we can use the lens formula to solve this problem. The lens formula is given by:

1/f = 1/v - 1/u

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

Given in the problem: f = 20 cm (convex lens so focal length is positive) u = -30 cm (object is on the same side as the light source, so distance is negative)

Substituting these values into the lens formula gives:

1/20 = 1/v - (-1/30)

Solving this equation for v gives:

1/v = 1/20 + 1/30

To add these fractions, find a common denominator, which is 60:

1/v = 3/60 + 2/60

Adding these fractions gives:

1/v = 5/60

Solving for v gives:

v = 60/5

So, v = 12 cm.

Therefore, the image is formed 12 cm on the other side of the lens from where the object is placed.

This problem has been solved

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