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Practice for u, a help for me 2

Some problems from geometric optics

Q1) Two mirrors are inclined at an angle \(\alpha\).Light ray is inclined parallel to one og the mirrors.The ray will start retracing its path after third reflection if \(\alpha=\) .The figure is above

Q2) A point object is kept in front of a plane mirror. The plane mirror is doing SHM of amplitude \(2~ cm\).The plane mirror moves along the \(x-axis\) and \(x-axis\) is normal to the mirror.The amplitude of the mirror is such that the object is always in front of mirror.The amplitude of SHM of the image is

Q3) A person's eye is at height of \(1.5~m\). He stands in front of a \(0.3~m\) long plane mirror which is \(0.8~m\) above the ground. the length of the image he sees of himself is

Q4) A person is standing in a room of width \(200~cm\). A plane mirror of vertical length \(10~cm\) is fixed on a wall in front og the person. The person looks into the mirror from distance \(50~cm\).How much width of the wall behind him will he able to see (assume that he uses the full mirror).

Q5) An unnumbered wall clock shows time \(04:25:37\), where \(1st\) terms represent hours,\(2nd\) represent minutes and \(3rd\) represents seconds. What time will its image in a plane mirror show..

Note by Tanishq Varshney
1 year, 10 months ago

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For problem 1 and 2 check the first image, I'll explain problem 3(answer for 1 is 30 degrees)

At first and a ray from A to top end of mirror after reflection it will hit C(C will be at distance .8m from A), Now similarly send a ray to bottom end, after reflection it will hit E(E is at a distance 1.4m from A) and he can see himself from C to E which equals 0.6m.

Similarly in problem 4 send ray to ends of mirror and apply simple geometr(our answer = 2x + 10 = 50)

For problem 5 answer is equivalent when you put mirror on axis containing numbers 6 and 12.

Pro tip: In mostly all plane mirror problems you just need to send rays at extremities of mirror and apply simple geometry. Krishna Sharma · 1 year, 10 months ago

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Comment deleted Mar 25, 2015

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@Tanishq Varshney Hi

Did you have doubts in these questions or did you want to test us ? I am just curious ! Azhaghu Roopesh M · 1 year, 10 months ago

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@Azhaghu Roopesh M He would have posted it as a question to test us Rohit Shah · 1 year, 10 months ago

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@Rohit Shah I see , but these questions were a bit easy .

I wanted to ask you this , what does your profile pic depict ? I can only guess that it's a fabric of some sort , which has been hand stitched, as evident from the fact that you have used it a a profile pic , by you (perhaps) ,and the lines aren't quite straight so I'm guessing you are inexperienced at it .

Please tell me I am wrong !

Btw I did it just for fun :) Azhaghu Roopesh M · 1 year, 10 months ago

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@Azhaghu Roopesh M That is a fabric rather a sofa cover which I had uploaded initially. But then I didn't change it later. I agree that its absolutely meaningless. Rohit Shah · 1 year, 10 months ago

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@Rohit Shah Aww! So I made a wrong deduction! :(

Here I thought that you had posted a piece of your work . That's why I don't make these guesses online . Azhaghu Roopesh M · 1 year, 10 months ago

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1) 30 2) 4 cm 3) 0.6 m 4) 50 cm 5) 7:34:23 Rohit Shah · 1 year, 10 months ago

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@Rohit Shah

  1. 30 degrees.
Krishna Sharma · 1 year, 10 months ago

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@Rohit Shah 1) 30 degrees and 5) 7:34:23. Tanishq Varshney · 1 year, 10 months ago

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@Tanishq Varshney You are correct I did a silly mistake in both. I realized later Rohit Shah · 1 year, 10 months ago

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@Rohit Shah can u explain me the 5) one Tanishq Varshney · 1 year, 10 months ago

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@Tanishq Varshney Just draw the clock and reflect . Or you could subtract 12 hours from the given time(its effectively the same thing) Rohit Shah · 1 year, 10 months ago

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@Rohit Shah then how is 25 replaced by 34 , why isnt it 35 Tanishq Varshney · 1 year, 10 months ago

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@Tanishq Varshney Because the seconds add up to give an extra minute. 37 + 23 is the extra minute. You could have used a similar reasoning that 4 + 7 is not 12 but we actually have got an extra hour by adding 25 and 35 mins. So sudeep has suggested a fast way of subtracting 12 hours Rohit Shah · 1 year, 10 months ago

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@Tanishq Varshney Another simple way which prevents confusion is that you subtract the given time from \( 11: 59 : 60 \) component wise. So here \( 11:59:60 - 04:25:37 = 07:34:23 \) which is the required answer. Sudeep Salgia · 1 year, 10 months ago

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@Sudeep Salgia Yeah, this is indeed the best way out . Azhaghu Roopesh M · 1 year, 10 months ago

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@Deepanshu Gupta @Rohit Shah @Azhaghu Roopesh M @Raghav Vaidyanathan ,plz post a solution for the above problems Tanishq Varshney · 1 year, 10 months ago

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