Question

If the length of the object is 5cm, the distance between the pinhole and the object is 2cm and the distance between the pinhole and the screen is 4cm, Find the size of the image.​

Answer 1

Given :-

• Height of object = 5cm

• Distance of object = 2cm

• Distance of image = 4cm

To Find :

• Height of image

Solution :-

We know that, magnification is defined as the ratio of distance of image to the distance of object.

• m = -v/u

Where v = distance of image and u = distance of object.

By substituting the values, we get

→ m = -4/2

→ m = -2

Also we know that, m = h'/h

where h' = distance of image and h = distance of object

→ m = h'/5

→ -2 = h'/5

→ h' = -10 cm

Negative sign shows that image is real and inverted.

Answer 2

Given :-

☄ Height of object, h = 5cm

☄ Distance of object, u = 2cm

☄ Distance of image, v = 4cm

To Find :-

size of the image

Solution :-

We know that,

The linear magnification produced by the mirror is equal to the ratio of the image distance to the object distance, with a minus sign. .i.e.,

• m = -v/u

here, v = distance of image and u = distance of object.

so,

➠ m = -v/u

➠ m = -4/2

➠ m = -2

The ratio of height of image to the height of object is known as linear magnification. .i.e.,

• m = h'/h

here, h' = distance of image and h = distance of object

so,

➠ m = h'/h

➠ m = h'/5

➠ -2 = h'/5

➠ h' = -10 cm [ -ve sign detects that the image is real and inverted]

Thus, the size of the image is -10cm.

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