A student investigates the magnification of the image produced by a thin converging lens using an optical bench setup.
An illuminated shape of height hO=1.8 cmh_{\text{O}} = 1.8\text{ cm}hO=1.8 cm is used as the object. A screen is moved along the bench until a sharp image of the object is formed.
If the magnification m m\,m is 4.00, calculate the height of the image, hIh_{\text{I}}hI, formed on the screen.
The student records the object distance u u\,u and the image distance v v\,v for various positions. The data are shown in the table below:
| u / cmu\text{ / cm}u / cm | v / cmv\text{ / cm}v / cm | mmm |
|---|---|---|
| 15.0 | 59.8 | |
| 18.0 | 36.3 | |
| 24.0 | 24.2 | |
| 30.0 | 19.9 | |
| 36.0 | 18.1 |
Calculate the magnification m m\,m for each value of u u\,u using the equation m=vu\displaystyle m = \frac{v}{u}m=uv. Record the values of m m\,m to 2 decimal places.
When the student plots a graph of u / cmu\text{ / cm}u / cm (y-axis) against mmm (x-axis), they determine the value of the object distance u1 u_1\,u1 at which the magnification m=1.00m = 1.00m=1.00 is exactly 24.1 cm. Use this value of u1 u_1\,u1 to calculate the focal length f f\,f of the lens using the equation:
f=u12 f = \frac{u_1}{2} f=2u1State two practical precautions that should be taken in this experiment to obtain accurate readings.
216 exam-style questions on CIE IGCSE Physics 3.2 Light, covering 3.2.1a Reflection of light, 3.2.1b Images in a plane mirror, 3.2.2 Refraction of light, 3.2.2a Refraction of light, 3.2.2b Total internal reflection, 3.2.2c Refractive index and critical angle, 3.2.2d Optical fibres, 3.2.3a Converging and diverging lenses, 3.2.3b Ray diagrams and the nature of images, 3.2.3c Virtual images and the magnifying glass, 3.2.3d Correcting long-sightedness and short-sightedness, and 3.2.4 Dispersion of light. Each one has a worked solution and a mark scheme showing where the marks go.