Table of Contents
Activity 11.10: Forming Images with a Convex Lens
Objective: To observe how a convex lens forms different types of images of a candle flame at various distances, illustrating the concepts of real and virtual image formation.
Materials Needed:
- A convex lens (a lens that is thicker in the middle and thinner at the edges).
- A candle.
- Matches or a lighter.
- A screen or a wall (for projecting real images).
Procedure:
- Light the Candle: Place the candle on a table and light it. Make sure it’s placed safely.
- Close-Up Observation: Begin with the candle placed very close to the convex lens, within its focal length. Observe the image formed by the lens.
- Change the Distance: Gradually move the candle away from the lens. Watch how the image changes as the candle moves from within the focal length, to at the focal length, and beyond it.
- Use the Screen: When the candle is beyond the focal length, try projecting the image on a screen. Observe the characteristics of the image.
Also Check – Class 7 Science -Chapter 15 – Light- Complete Notes
Also Check – Chapter 11- A Detailed Guide to the Light Activities for Class 7 Students
Core Concepts Explained:
- Convex Lenses and Image Formation: Convex lenses can bend (refract) light rays to form images. The nature of these images depends on the distance of the object (candle flame) from the lens.
- Real Images:
- Formed when the object is beyond the focal length of the lens.
- Can be projected on a screen.
- They are inverted (upside down) and their size varies depending on the distance from the lens.
- Virtual Images:
- Formed when the object is within the focal length of the lens.
- Cannot be projected on a screen; they seem to be on the same side of the lens as the object.
- They are erect (upright) and larger than the object.
Also Check – Difference Between a Convex and Concave Lens
Possible Questions and Answers:
Why does the image change size and orientation as I move the candle?
- The position of the candle relative to the lens’s focal length determines how the lens refracts (bends) the light rays, leading to different types of images.
Also Check – Convex Lenses- Principles, Applications, and Insights
Why can’t I project the virtual image on a screen?
- Virtual images are formed by the apparent divergence of light rays; they aren’t real convergence points in space, so you can’t project them.
What does ‘beyond the focal length’ mean?
- This means the candle is placed at a distance from the lens that is greater than the distance between the lens and its focal point.
Why does the image become upside down?
- When the candle is beyond the focal length, the lens refracts the light in such a way that the top of the flame appears at the bottom and vice versa, creating an inverted image.
Will any convex lens work for this activity?
- Yes, any convex lens will work, but the focal length might vary, which will affect the distance where you’ll see the image changes.
