Convex Mirror - Focal Length

Materials Required:

• Illuminated wire gauze
• Stand
• Screen
• Meter scale
• Convex lens
• Given convex mirror

Real Lab Procedure:

• Place a convex lens on a stand facing the illuminated wire gauze at a fixed distance, say 30 cm, away from the wire gauze.
• Place a screen, at the other side of the lens so that the wire gauze, lens and screen are in a straight line.
• Adjust the position of screen to get a clear image of the wire gauze.
• Now fix the given convex mirror to another stand and place it in between the convex lens and screen with its reflecting face facing the wire gauze.
• Now place another side by side with the wire gauze.
• The position of the convex mirror is adjusted so that a clear image of the wire gauze is formed on the screen placed side by side with the wire gauze.
• Measure the distance between the mirror and first screen and take as the radius of curvature of the mirror R.

• The focal length of the mirror is calculated as ,

$f = \frac{Radius \ of \ Curvature \ (R)}{2}$

• Repeat the experiment by moving the convex lens towards the object by 2 cm each time and record the values in a tabular column.

Simulator Procedure (as performed through the Online Labs):

• Select the mirror from the drop down list.
• To insert the convex lens in front of the wire gauze, click on the ‘Insert convex lens’ button.
• Select the position of the convex lens using the slider.
• To turn on the wire gauze, click on the ‘Light On’ button.
• Adjust the position of the screen using the slider.
• When clear image is formed, you can see a popup.
• Now click on ‘Insert convex mirror’ button to insert the convex mirror in between the wire gauze and the screen.
• Adjust the position of the mirror using the slider to get a clear image of the wire gauze on the screen placed side by side with the wire gauze.
• You can measure the radius of curvature (R) of the mirror by measuring the distance between convex mirror and the screen placed behind the mirror.
• You can calculate the focal length of the mirror using the equation f = R/2.
• You can verify you result by clicking on the ‘Show result’ button.
• To redo the experiment, click on the ‘Reset’ button.

Observations:

 SI No. Distance from lens to Radius of curvature, R (cm) Focal length of the Convex Mirror f =R/2 Object u (cm) Image v (cm) 1 2 3 4 5

Calculation:

Focal length of the convex mirror, Mean (f) = ------cm

Result:

The focal length of the given convex mirror = ……………….cm

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