Question

The focal length of the lens of a simple film camera is 40. 0 mm. By what amount should the distance between the lens and the film be increased or decreased to change the focus from a person who is 25 m from the lens to one who is 4. 0 m from the lens?.

Answer 1

0.4 mm

The distance should be increased by 0.4 mm.

We use lens formula here,

$\frac{1}{f}$ = $\frac{1}{v}$ - $\frac{1}{u}$

where,

f =  focal length

u = distance of the object

v = distance of the image formed

Given that,

f = 40 mm

u = 4 m = 4000 mm

v = ?

Using the lens formula, we get:

$\frac{1}{f}$ = $\frac{1}{v}$ - $\frac{1}{u}$

$\frac{1}{40}$ = $\frac{1}{v}$ - $\frac{1}{4000}$

$\frac{1}{v}$ = $\frac{1}{40}$ + $\frac{1}{4000}$

v = 39.6 mm

Change in the distance = 40 - 39.6

                                        = 0.4 mm

Therefore, the distance has to be increased by 0.4 mm

What is lens formula?

• For a spherical mirror, the focal length, image distance, and object distance are all related by the lens equation, often known as the lens formula.
• The formula is presented as follows: Lens Formula - 1/u + 1/v = 1/f, where v is the image's distance from the lens.

The purpose of the lens formula:

• The well-designed lens formula can be used for both concave and convex lenses.
• The lens formula is used to determine the focal length, picture type, and image distance.

T o learn more the lens formula visit:

brainly.com/question/2098689

#SPJ4

Answer 2

The distance should be increased by 0.4 mm.

Calculation:

Lens formula is used here.

What is the lens formula?

For a spherical mirror, the focal length, image distance, and object distance are all related by the lens equation, often known as the lens formula.

It is given by,

$\frac{1}{f} = \frac{1}{v} -\frac{1}{u}$

where,

f = focal length

u = distance of the object

v = distance of the image formed

Given,

f = 40 mm

u = 4 m = 4000 mm

v =?

Using the lens formula,

$\frac{1}{f} = \frac{1}{v} -\frac{1}{u}$

$\frac{1}{40} = \frac{1}{v} -\frac{1}{4000}$

$\frac{1}{v} = \frac{1}{40} + \frac{1}{4000}$

v = 39.6 mm

Change in distance = 40 - 39.6

                                 = 0.4 mm

Hence, the distance should be increased by 0.4 mm.

Learn more about the lens formula here:

brainly.com/question/13063265

#SPJ4