write an activity to find focal length of a concave mirror .
The Correct Answer and Explanation is:
Activity to Find the Focal Length of a Concave Mirror
Aim:
To determine the focal length of a concave mirror using the distant object method.
Apparatus Required:
- Concave mirror
- Mirror stand
- Meter scale or measuring tape
- Screen
- Distant object such as a building or tree
Procedure:
- Place the concave mirror on the stand in an open area where a distant object is visible, preferably more than 50 meters away.
- Position the screen in front of the mirror and adjust its distance until a clear, sharp image of the distant object appears on the screen.
- The image formed will be real, inverted, and diminished.
- Measure the distance between the mirror and the screen using the meter scale.
- Record this distance as the focal length of the concave mirror.
- Repeat the procedure three times to get accurate readings.
- Calculate the average of the three measured distances to find the final focal length.
Conclusion:
The average distance between the mirror and the screen gives the focal length of the concave mirror.
Explanation
A concave mirror is a spherical mirror with its reflective surface curved inward, resembling a portion of the inner surface of a sphere. It has the property of converging light rays that are parallel to its principal axis. This unique characteristic makes it suitable for applications such as shaving mirrors, solar concentrators, and in optical devices.
The focal length of a concave mirror is the distance between its pole (the center of its surface) and its focus (the point where parallel rays converge after reflection). To find this focal length practically, the distant object method is a simple and effective technique.
Distant objects, such as buildings or trees located far away, can be considered sources of parallel rays of light. When these rays strike the concave mirror, they reflect and converge at the focal point. By placing a screen in front of the mirror and adjusting its position, one can locate the sharp, real, and inverted image formed by the mirror. The distance between the mirror and the screen at this position is the focal length.
Since the object is at a considerable distance, we assume its distance to be infinite, simplifying the calculation. The image thus forms at the focal point of the mirror. Repeating the activity several times and averaging the results increases the accuracy of the measurement.
This method is widely used in basic physics experiments to help students understand the nature of curved mirrors and how they manipulate light.
