Question

4. How far should an object be from the pole of a concave mirror of focal length 20 cm to form a real ima
1
th of the size of the object.​

Answer 1

$\huge\underline{\overline{\mid{\bold{\red{ANSWER-}}\mid}}}$

f = -20

m = -v/ u

-1 / 5 = - v / u

v = u / 5 .......... 1

1 / f = 1 / v +1 / u

1 / -20 = 5 / u + 1 / u ( from 1 )

-1 / 20 = 6 / u

u = 6 *(-20)

u = -120

therefore the object is 120cm away from the pole

Answer 2

$\huge{\red{\overline{\underline{\mathtt{\mid{ANSWER{\mid}}}}}}}$

f = -20

m = -v/ u

-1 / 5 = - v / u

v = u / 5 .......... 1

1 / f = 1 / v +1 / u

1 / -20 = 5 / u + 1 / u ( from 1 )

-1 / 20 = 6 / u

u = 6 *(-20)

u = -120

therefore the object is 120cm away from the pole

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