Continuing the A Level Physics revision series with geometric optics. The lens formula. Real and virtual images. Convex and Concave lenses and mirrors.
The relative size of the image to the object depends on where the object is originally placed. If it is within the focal length, then the image is usually larger.
Its at the point where the two lines cross after they have both been reflected. That is the point at which all rays (lines from the object) will converge (after reflection) to produce the image.
The last part seems a bit incorrect. If the object is placed at the focal point, for concave lens and convex mirror, a virtual image will still be formed. You can prove that with your sign conventions I think. It's only for convex lens and concave mirrors where the image is at +/- infinity.
Light traveling parallel to the focal plane will converge at the focal point. But that is not the case for other light rays. So an image does not necessarily form at the focal point
See my two videos on fluid dynamics. The first deals with upthrust (and Archimedes Principle) and the second deals with Stokes Law (its in the second half - after Bernoulli's Theorem.
I deal with this in my series on electromagnetic radiation, but in essence the light which crosses the boundary of the two media must satisfy Maxwell's 4 equations. These are called the boundary conditions between the two media. It is this which dictates Snell's Law.
Aperture is the size of the hole through which the light passes. If it is small then it will result in a much sharper image. But there will be less light so the image may be darker. A wider aperture allows in more light but may result in less focused image. On focal length it depends what you want. A telescope needs a long focal length and microscope needs a short focal length.
Thank youu!!!!!! These videos are amazing you sir are a very good teacher i like the way you actually explain why the formulae's are the way they are it makes sense its unfortunate my a level teachers dont do this but thanks a bunch i hope i start my exams of with good grades xD Im doing the OCR Edexecel exam on Materials and Mechnanics and the 2nd one Waves and Light.
hello. Thank you for this great video, it is very helpfull. I want to ask you a question, I have a system which i want to project one image and the image that i get has Pincushion distortion, how can i correct that distortion without using a postprocessing method? do i have to use other lens to invert that distortion? thank you
I have a question. How come the image doesn't form at the focal point. The focal point is the place where the light converges to a single point, shouldn't that be where the image forms? And if the image forms there, then the image distance v and focal length will always be the same. I just understand how if the light converges at the focal point what prevents the image from forming there.
Why does the light bend on refraction. I read that is because the speed of light is different in different medium. But it could continue in the same direction with slower speed. Why does the direction change?
The bit that confuses me it that at 15:37 you say "where these two points cross, that is where the image will be formed". That in itself makes sense, but the light rays cross more than once. In that diagram, the rays drawn cross twice, once where you say the image is and once between the mirror and the focal point, before one ray has been reflected. Why is there only one image formed, not two, and why is it at that crossing of the rays, not the other?
Hi Dr. physics, Can you explain reflection/absorption/transmission of light in atomic level? Why do matters absorb only specific frequencies of light and reflect or transmit the others. What makes matters reflect light and what makes them transmit it. In what atomic/molecular configuration of matters dictate the reflection coefficient/transmission coefficient/ absorption coefficient of light? Thank you in advance.
No the exact point of you that is in the focal point would, except not all of you can fit into that point can it? it is the size of a photon. the spot would be so incredibly small your brain would ignore it.
Hmm my what a sexy accent! Love the video very helpful! Optics is fairly challenging. I'm subscribing to your channel continue making amazing physics videos I ❤️ them
Sorry but where did you use sign convention when deriving the lens formula 1/u+1/v=1/f is the mirror formula not the lens formula The lens formula is 1/v-1/u=1/f It can be proved by either the lensmaker formula (refraction on a spherical surface) or by similar triangles using proper sign convention Using proper sign convention at 7:21 yields a/b=-u/v and -u/v=f/v-f which results in 1/f= u-v/uv=1/v - 1/u For a convex lens the first radius or R1 is positive which results in v and f being positive while u is negative for r1 For r2 u becomes positive while f becomes negative and so does v Everything else was correct Just use the proper Cartesian Sign Convention
Actually i made a mistake. The object distance is positive if it is measured against the direction of the light rays according to convention. The image distance is positive if it is measured in the direction of the light rays by convention. Which is why the image distance for virtual images is negative, because they appear on the side of the object, and so their distance is measured against the light ray direction. I think the sign should be positive in the formula... Uchiha Madara sama.
I'm a frst year medical student nd I watch ur videos bfr tests. dnt evn hv to study I ace them... thankyou. ur work is highly appreciated
How’s your medical journey going lol
I'M an optometry student ,i found your videos important for my training. thank you
This was so incredibly helpful, I would highly recommend it to any student trying to learn the concept :D
The relative size of the image to the object depends on where the object is originally placed. If it is within the focal length, then the image is usually larger.
you are so damn good at explaning stuff!
Thank you for providing us with such a well-done informative series of videos! It's helping a bunch with my upcoming Physics tests!
Its at the point where the two lines cross after they have both been reflected. That is the point at which all rays (lines from the object) will converge (after reflection) to produce the image.
The last part seems a bit incorrect. If the object is placed at the focal point, for concave lens and convex mirror, a virtual image will still be formed. You can prove that with your sign conventions I think. It's only for convex lens and concave mirrors where the image is at +/- infinity.
Light traveling parallel to the focal plane will converge at the focal point. But that is not the case for other light rays. So an image does not necessarily form at the focal point
See my two videos on fluid dynamics. The first deals with upthrust (and Archimedes Principle) and the second deals with Stokes Law (its in the second half - after Bernoulli's Theorem.
This is informative and easy to digest. Thank you.
I deal with this in my series on electromagnetic radiation, but in essence the light which crosses the boundary of the two media must satisfy Maxwell's 4 equations. These are called the boundary conditions between the two media. It is this which dictates Snell's Law.
Aperture is the size of the hole through which the light passes. If it is small then it will result in a much sharper image. But there will be less light so the image may be darker. A wider aperture allows in more light but may result in less focused image. On focal length it depends what you want. A telescope needs a long focal length and microscope needs a short focal length.
Fantastic video! Thank you
Thank youu!!!!!! These videos are amazing you sir are a very good teacher i like the way you actually explain why the formulae's are the way they are it makes sense its unfortunate my a level teachers dont do this but thanks a bunch i hope i start my exams of with good grades xD Im doing the OCR Edexecel exam on Materials and Mechnanics and the 2nd one Waves and Light.
How did you go?
Thanks for your uploads!
Hi!
Thank you very much. Easy to understand pronunciation. Very Useful information.
Regards from Spain
Good luck.
Well 1/f = -1/3 which means that f = -3. Thanks for kind comment.
Thanks for videos lessons, they have have helped so much , stay long master
hello. Thank you for this great video, it is very helpfull. I want to ask you a question, I have a system which i want to project one image and the image that i get has Pincushion distortion, how can i correct that distortion without using a postprocessing method? do i have to use other lens to invert that distortion? thank you
Good video.
great video very well explained
You save so many exam
at 3:50, the problem has two focal lengths? Because the ray twos focal length isn't going through ray 1's. and yet it can still form an image?
what a nice lecture.keep it up
it's really great explanation .. thanks a lot ...
BEAUTIFUL!
Thank you. You are a great teacher.
Very good! Congratulations!
not your business !!!!
I have a question. How come the image doesn't form at the focal point. The focal point is the place where the light converges to a single point, shouldn't that be where the image forms? And if the image forms there, then the image distance v and focal length will always be the same. I just understand how if the light converges at the focal point what prevents the image from forming there.
good job
Very informative, thanks a lot for the help!
mind- blowing!
thank you sir
Thank you so much for the video It helped me out so much for my exams!
Keep it up!!
Try finding the final image of an object through multiple compound lens and mirrors.
Great video, should have more views
How does the focal length and aperture affect the image ? Pls explain.
Thx a lot! I understand after watched this video!
Thank you
Well done sir, helped alot
works for my test thanks
Thanks alot
Why does the light bend on refraction. I read that is because the speed of light is different in different medium. But it could continue in the same direction with slower speed. Why does the direction change?
great job
The bit that confuses me it that at 15:37 you say "where these two points cross, that is where the image will be formed". That in itself makes sense, but the light rays cross more than once. In that diagram, the rays drawn cross twice, once where you say the image is and once between the mirror and the focal point, before one ray has been reflected.
Why is there only one image formed, not two, and why is it at that crossing of the rays, not the other?
It's amazing...
Thank you Physics God.
Hi Dr. physics,
Can you explain reflection/absorption/transmission of light in atomic level? Why do matters absorb only specific frequencies of light and reflect or transmit the others. What makes matters reflect light and what makes them transmit it. In what atomic/molecular configuration of matters dictate the reflection coefficient/transmission coefficient/ absorption coefficient of light?
Thank you in advance.
Neet video!
thank u so much! :)
Thank you sir!
THANK YOU
Thank you for the video! Can you please make a video on Fibre optic, Snell's law and total internal reflection. Than you
Syed ZA Tirmzi Covered here ruclips.net/video/AnnHLaBG2tg/видео.html
DrPhysicsA Also at the end of this video ruclips.net/video/gycff144mHw/видео.html
When are the string and M theory vids coming out???
All this makes sense after toying around with DSLR camera lenses.
Isn’t it 1/v= 1/u + 1/f ?
Thanks a lot for explaining! The physics teacher in the French school I attend has a terrible English...
sir, when we calculated focal length at 25:00, shouldnt we apply cartesian sign conventions?
+Akshay Mohan Sign convention is pretty much up to you, as long as you are consistent.
okk :)
Nice video.. Can't help laughing when you're saying "leeeeens" though ;)
@DrPhysicsA could you please do a video on Stokes Law and Upthrust PLEASE :(
real is positive
geometrical optics please can you do Under Title in French
Convex lenses look like vaginas
btw, great video, thank you
At 25.03 minutes, doesnt he make a mistake when saying that 1+3/6 is equal to 1.5?
((1+3)/6)^-1
Isn't geometry fascinating?
lennnzzz xD no but this video is really helpful, thank you!
Alas, I'm not really up to the technical aspects of this. Perhaps someone else will know.
So I'll be invisible if i was standing in front of a Concave and Convex mirror in its exact focal point of light ? Hmm
No the exact point of you that is in the focal point would, except not all of you can fit into that point can it? it is the size of a photon. the spot would be so incredibly small your brain would ignore it.
Hmm my what a sexy accent! Love the video very helpful! Optics is fairly challenging. I'm subscribing to your channel continue making amazing physics videos I ❤️ them
this video helped me beyond belief. Thank you so much. I love your channel so much. You are brilliant !!
misssweethearted Thats very kind. If you were doing exams I hope they went well.
excellent
240p in the year 2015? :D
thetastefulchoice 2012!
Sorry but where did you use sign convention when deriving the lens formula
1/u+1/v=1/f is the mirror formula not the lens formula
The lens formula is 1/v-1/u=1/f
It can be proved by either the lensmaker formula (refraction on a spherical surface) or by similar triangles using proper sign convention
Using proper sign convention at 7:21 yields a/b=-u/v and -u/v=f/v-f which results in 1/f= u-v/uv=1/v - 1/u
For a convex lens the first radius or R1 is positive which results in v and f being positive while u is negative for r1
For r2 u becomes positive while f becomes negative and so does v
Everything else was correct
Just use the proper Cartesian Sign Convention
+Feitan UCHIHA The object distance is naturally negative i.e the substituted value of u is negative.
+KAMOGELO THOKWANE I know
The formula is correct but proper sign convention should be used
Actually i made a mistake. The object distance is positive if it is measured against the direction of the light rays according to convention. The image distance is positive if it is measured in the direction of the light rays by convention. Which is why the image distance for virtual images is negative, because they appear on the side of the object, and so their distance is measured against the light ray direction. I think the sign should be positive in the formula... Uchiha Madara sama.
be my teacher