| Aim | To find the focal length of a convex lens by plotting graphs between u and v or between 1/u and 1/v. |
| Apparatus Required | A convex lens A light source (such as a light bulb or a laser) A screen or a piece of paper to capture the image A ruler or measuring tape A stand to hold the lens and the light source An object (such as a pencil or a coin) |
| Theory | A convex lens is a lens that converges light rays. The focal length of a convex lens is the distance between the lens and its focal point. To find the focal length of a convex lens, we can use the formula 1/f = 1/u + 1/v, where f is the focal length of the lens, u is the distance between the object and the lens, and v is the distance between the image and the lens. We can plot a graph between u and v or between 1/u and 1/v to determine the focal length of the lens. |
| Procedure | Set up the apparatus by placing the convex lens on the stand, and the light source on one side of the lens. Place the screen or piece of paper on the opposite side of the lens, so that it can capture the image formed by the lens. Place an object (such as a pencil or a coin) at a known distance u from the lens. Adjust the position of the screen or paper until a clear and sharp image of the object is formed on it. Measure the distance v between the screen and the lens. Repeat steps 3 to 5 for different values of u, ranging from near the focal point to infinity. Record the values of u and v for each measurement. |
| Observation and Result | Observation: As the object is moved closer to the lens, the image distance v decreases. When the object is placed at the focal point of the lens, the image distance becomes infinite. When the object is placed between the focal point and the lens, the image distance becomes negative, indicating that the image is virtual and upright. As the object is moved further away from the lens, the image distance increases. The values of u and v can be plotted on a graph, with u on the x-axis and v on the y-axis. The graph should show a curve that intersects the x-axis at the focal point of the lens. Alternatively, the values of 1/u and 1/v can be plotted on a graph, with 1/u on the x-axis and 1/v on the y-axis. The graph should show a straight line, with the slope of the line equal to the reciprocal of the focal length of the lens. Result: The focal length of the convex lens can be calculated using the formula 1/f = 1/u + 1/v, where u is the distance between the object and the lens, and v is the distance between the image and the lens. The values of u and v for different measurements can be plotted on a graph, with u on the x-axis and v on the y-axis. The graph should show a curve that intersects the x-axis at the focal point of the lens. Alternatively, the values of 1/u and 1/v can be plotted on a graph, with 1/u on the x-axis and 1/v on the y-axis. The graph should show a straight line, with the slope of the line equal to the reciprocal of the focal length of the lens. |
