Thin Lens Equation Quiz with Answers: Test Your Knowledge

📚 Quick Study Guide

• 🔍 The thin lens equation relates the object distance ($d_o$), image distance ($d_i$), and focal length ($f$) of a lens: $\frac{1}{f} = \frac{1}{d_o} + \frac{1}{d_i}$.
• 📏 Object distance ($d_o$) is the distance from the object to the lens. It's usually positive.
• 🖼️ Image distance ($d_i$) is the distance from the image to the lens. It's positive for real images and negative for virtual images.
• 🔭 Focal length ($f$) is the distance from the lens to the focal point. It's positive for converging lenses and negative for diverging lenses.
• 📈 Magnification ($M$) is the ratio of the image height ($h_i$) to the object height ($h_o$): $M = \frac{h_i}{h_o} = -\frac{d_i}{d_o}$.
• 💡 A positive magnification indicates an upright image, while a negative magnification indicates an inverted image.
• 📝 Sign conventions are crucial for using the thin lens equation correctly.

🧪 Practice Quiz

1. Question 1: A lens has a focal length of 20 cm. An object is placed 30 cm from the lens. What is the image distance?
   1. 10 cm
   2. 30 cm
   3. 60 cm
   4. 40 cm
2. Question 2: An object is placed 15 cm from a lens. The image is formed 30 cm from the lens on the opposite side. What is the focal length of the lens?
   1. 5 cm
   2. 10 cm
   3. 15 cm
   4. 20 cm
3. Question 3: A lens produces a virtual image that is twice the size of the object. If the object is 10 cm from the lens, what is the image distance?
   1. -5 cm
   2. -10 cm
   3. -15 cm
   4. -20 cm
4. Question 4: A converging lens has a focal length of 25 cm. If an object is placed 50 cm away, what is the magnification?
   1. -1
   2. 1
   3. 0.5
   4. -0.5
5. Question 5: A diverging lens has a focal length of -10 cm. An object is placed 20 cm from the lens. What is the image distance?
   1. -6.67 cm
   2. 6.67 cm
   3. 30 cm
   4. -30 cm
6. Question 6: If the magnification of a lens is -0.5 and the image distance is 15 cm, what is the object distance?
   1. 7.5 cm
   2. -7.5 cm
   3. 30 cm
   4. -30 cm
7. Question 7: A lens forms a real, inverted image twice the size of the object. If the object is 20 cm from the lens, what is the focal length?
   1. 10 cm
   2. 13.33 cm
   3. 20 cm
   4. 40 cm