Question

Describe the image of a candle positioned 20cm in front of a concave mirror of focal length 30cm.

virtual, inverted, 12cm behind mirror and magnified 3 times
real, inverted, 12cm in front of mirror and diminished 3 times
virtual, erect, 60cm behind mirror and magnified 3 time
real, erect, 60cm in front of mirror and diminished 3 times

Answer 1

Answer on Question #46513, Physics, Other

Task:

Describe the image of a candle positioned $20\mathrm{cm}$ in front of a concave mirror of focal length $30\mathrm{cm}$ .

- virtual, inverted, 12cm behind mirror and magnified 3 times

real, inverted, 12cm in front of mirror and diminished 3 times

virtual, erect, 60cm behind mirror and magnified 3 time

real, erect, 60cm in front of mirror and diminished 3 times

Answer:

Focal length (f) = - 30 cm

The distance between the object and the mirror $(u) = -20\mathrm{cm}$

The distance between the image and the mirror $(\nu) = ?$

$$\begin{array}{l} - \frac {1}{f} = \frac {1}{v} + \frac {- 1}{u} \\ - \frac {1}{3 0} = \frac {1}{v} + \frac {- 1}{2 0} \Rightarrow \frac {1}{v} = \frac {1}{6 0} \Rightarrow v = 6 0 c m \\ \end{array}$$

Let the size of the object be equal to $x$ .

Given size of the image $= y$ .

But we know that $\frac{y}{x} = \frac{v}{u} = 3$

So the image of a candle virtual, erect, 60cm behind mirror and magnified 3 time.

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