A small lightbulb is 1.10 m from a screen. Part A If you have a convex lens with

Question

A small lightbulb is 1.10 m from a screen.

Part A

If you have a convex lens with 17 cm focal length, where are the two lens locations that will project an image of the lightbulb onto the screen?

Express your answers using two significant figures separated by a comma.

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Part B

What’s the magnification in the first case (smaller distance from the lightbulb)?

Express your answer using two significant figures.

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Part C

What’s the magnification in the second case (larger distance from the lightbulb)

A small lightbulb is 1.10 m from a screen.

Part A

If you have a convex lens with 17 cm focal length, where are the two lens locations that will project an image of the lightbulb onto the screen?

Express your answers using two significant figures separated by a comma.

between the lightbulb and the screen at d1, d2=   cm from the lightbulb

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Part B

What’s the magnification in the first case (smaller distance from the lightbulb)?

Express your answer using two significant figures.

M =

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Part C

What’s the magnification in the second case (larger distance from the lightbulb)

Explanation / Answer

Diistance of light bulb from screen = 1.10 m

Let the lens be placed at distance u from light bulb towards the screen

The focal length of lens = 17 X 10^(-2) mrs

Let the distance from lens to screen be v = 1.10- u

For the lens f

f = uv/(u+v) = u ( 1.10- u)/ 1.10

17 X 10^(-2) X 1.10 = 1.10 u - u^2

u^2- 1.10 u +0.187 =0

The above is quadratic equation in u, with two solutions for u

u1 = 0.89 mrs = 89 cm  

u2 = 0.21 mrs = 21cm

When u2 position is considered ,v 2 = 0.89 mrs

magnification = - v/u=0.89 mrs/0.21 mrs = - 4.2, showing a image magnified 4.2 times the object

The negative in magnification signifies the image is inverted.

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