How to Solve IGCSE Lens q with Unspecified Distance

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In summary: My apologies.In summary, the conversation discusses the requirements for a sketch diagram in order to solve a question about the placement of an object in relation to a lens. The problem states that the width of the beam before it reaches the lens is 1.0 cm and the question is to find the distance(s) on the other side of the lens where the beam is less or more than 1.0 cm. The speaker also mentions the need to show some work or intention to answer the question. The conversation ends with a suggestion to draw a sketch and consider the given statement of the problem.
  • #1
S2100595
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Homework Statement
Could you please help me to figure out this question? The answer scheme says i) should be between 0 and 5.6 cm and ii) should be beyond 5.6 cm.
Relevant Equations
Not applicable
I know a sketch diagram is required for the question but they haven't specified the distance from the beam to the lens. They've just given the height of the beam. So how do I know how far I should place the object? Should the object (beam) be at infinity?
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  • #2
Read the problem. It clearly states that the width of the beam before it reaches the lens is 1.0 cm. So the question is to find the distance(s) on the other side of the lens where the beam is less or more than 1.0 cm. Should you require additional help, our rules require that you show some work or at least how you intend to answer this question.
 
  • #3
kuruman said:
Read the problem. It clearly states that the width of the beam before it reaches the lens is 1.0 cm. So the question is to find the distance(s) on the other side of the lens where the beam is less or more than 1.0 cm. Should you require additional help, our rules require that you show some work or at least how you intend to answer this question.
I have re-written how I intend to solve it
 
  • #4
S2100595 said:
I have re-written how I intend to solve it
Please don't edit your original post if you wish to reply. It could be confusing and is bad form. Start a new post. If you intend to draw a sketch, then draw one and post it. Mind the statement of the problem that says "A beam of parallel light strikes a converging lens of focal length 2.8 cm." What distance do you need to be given to draw a sketch of that?
 
  • #5
Alright never mind. This is my first post and I didn't realize there are so many restrictions and rules about how I can post on this forum.
 

FAQ: How to Solve IGCSE Lens q with Unspecified Distance

How do I determine the focal length of the lens if the distance is not specified?

To determine the focal length of the lens without a specified distance, you can use the lens formula: 1/f = 1/v - 1/u, where f is the focal length, v is the image distance, and u is the object distance. If either the object distance (u) or image distance (v) is provided, you can rearrange the formula to solve for the focal length (f).

What should I do if neither the object distance nor the image distance is given?

If neither the object distance (u) nor the image distance (v) is given, you will need additional information to solve the problem. Look for clues in the problem statement, such as the magnification, size of the object and image, or any special conditions like the lens being used in a specific setup (e.g., a projector or camera).

How can I use magnification to solve lens problems with unspecified distances?

Magnification (m) is given by the formula m = v/u, where v is the image distance and u is the object distance. If you know the magnification and either the object or image distance, you can use this relationship to find the missing distance and then apply the lens formula to find the focal length.

What assumptions can I make to simplify solving lens problems?

In some cases, you might need to make reasonable assumptions to simplify the problem. For example, if the problem involves a thin lens and no distances are specified, you might assume that the object is placed at a distance much greater than the focal length, making the image distance approximately equal to the focal length. However, always check if such assumptions are justified based on the context of the problem.

Are there any specific strategies for solving lens problems on the IGCSE exam?

Yes, there are a few strategies you can use:1. Carefully read the problem to identify any given information or clues.2. Use the lens formula and magnification formula as needed.3. Draw a ray diagram to visualize the problem and understand the relationships between the object, lens, and image.4. Check your final answer for consistency with the given information and the principles of optics.5. Practice with a variety of problems to become familiar with different scenarios and types of questions.

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