Please could I have a bit of help with Part C of this question (https://isaacphysics.org/questions/parabolic_mirror_r1?stage=all)? Maybe I’m just missing something obvious, but I’ve had no luck with it so far…

The ray diagram for a newtonian telescope with eyepiece looks like...

https://img-nm.mnimgs.com/img/study_content/content_ck_images/images/vn.png

so in order for the rays leaving the eyepiece to be parallel, the distance from the focal point of the primary mirror to the eyepiece lens is the focal length of the eyepiece lens.

https://img-nm.mnimgs.com/img/study_content/content_ck_images/images/vn.png

so in order for the rays leaving the eyepiece to be parallel, the distance from the focal point of the primary mirror to the eyepiece lens is the focal length of the eyepiece lens.

Original post by Joinedup

The ray diagram for a newtonian telescope with eyepiece looks like...

https://img-nm.mnimgs.com/img/study_content/content_ck_images/images/vn.png

so in order for the rays leaving the eyepiece to be parallel, the distance from the focal point of the primary mirror to the eyepiece lens is the focal length of the eyepiece lens.

https://img-nm.mnimgs.com/img/study_content/content_ck_images/images/vn.png

so in order for the rays leaving the eyepiece to be parallel, the distance from the focal point of the primary mirror to the eyepiece lens is the focal length of the eyepiece lens.

sillycon is this a similar approach to how you solved part b?

I am unable to solve it.

I am unable to solve it.

Original post by mosaurlodon

sillycon is this a similar approach to how you solved part b?

I am unable to solve it.

I am unable to solve it.

(edited 1 month ago)

Thank you! I've managed to get the answer now .

Actually please could I have a little more help with part c?

I must be drawing my diagram wrong because I am a little confused on how the distance from the lens to the focal point could be 1.4cm - could you please point out the flaw:

I must be drawing my diagram wrong because I am a little confused on how the distance from the lens to the focal point could be 1.4cm - could you please point out the flaw:

(edited 1 month ago)

Original post by mosaurlodon

Actually please could I have a little more help with part c?

I must be drawing my diagram wrong because I am a little confused on how the distance from the lens to the focal point could be 1.4cm - could you please point out the flaw:

I must be drawing my diagram wrong because I am a little confused on how the distance from the lens to the focal point could be 1.4cm - could you please point out the flaw:

I'll be honest I still am a little confused.

I understand that the distance between the lens and focal point is 'f' so I just need to work out 'x'.

So I thought the only way of working out 'x' would be to use similar triangles since I had no other idea of how to work out 'x'.

EDIT: in the diagram it should be 75.1 - but its still the wrong answer.

I understand that the distance between the lens and focal point is 'f' so I just need to work out 'x'.

So I thought the only way of working out 'x' would be to use similar triangles since I had no other idea of how to work out 'x'.

EDIT: in the diagram it should be 75.1 - but its still the wrong answer.

(edited 1 month ago)

Original post by mosaurlodon

I'll be honest I still am a little confused.

I understand that the distance between the lens and focal point is 'f' so I just need to work out 'x'.

So I thought the only way of working out 'x' would be to use similar triangles since I had no other idea of how to work out 'x'.

EDIT: in the diagram it should be 75.1 - but its still the wrong answer.

I understand that the distance between the lens and focal point is 'f' so I just need to work out 'x'.

So I thought the only way of working out 'x' would be to use similar triangles since I had no other idea of how to work out 'x'.

EDIT: in the diagram it should be 75.1 - but its still the wrong answer.

Well, if the light were reflected closer to the top of the plane mirror then it would travel a shorter distance before converging, but it would have travelled a longer distance to reach the plane mirror - so is the distance travelled the same?

ie red line length = orange line length?

ie red line length = orange line length?

Original post by mosaurlodon

Well, if the light were reflected closer to the top of the plane mirror then it would travel a shorter distance before converging, but it would have travelled a longer distance to reach the plane mirror - so is the distance travelled the same?

ie red line length = orange line length?

ie red line length = orange line length?

Oh I understand what you're hinting at now! Thanks so much! - Im sorry for wasting your time - I really overcomplicated this.

Original post by mosaurlodon

Oh I understand what you're hinting at now! Thanks so much! - Im sorry for wasting your time - I really overcomplicated this.

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