## King 3 years ago A fish in an aquarium approaches the left wall at a rate of 3 m/s and observes a fly approaching it at 8 m/s. If the refractive index of water is 4/3, find the actual velocity of the fly.Explain with steps..pls help!!!:(

Is it 4 m/s?

2. King

actual velocity of fly=3.75m/s

We know that, Speed of light in air / Speed of light in water = 4/3 Or, 3 * 10^8 / x = 4/3 Or, x = 2.25 * 10^8 Now, 2.25*10^8 = 3 So, 3*10^8 = 3/(2.25 * 10^8) * 3*10^8 = 9/2.25 = 4

Not getting how it is 3.75 m/s

5. King

wait hw is 2.25*10^8=3?

I just equated for the sake of unitary method, since fish is in water. It may be wrong.

7. Ishaan94

|dw:1332857679054:dw|

8. King

ok the ray refracts twice so?

9. Ishaan94

so, get me the refractive index of Glass...

10. King

hw?

11. Ishaan94

arre book mein dheko na

12. King

oh..i dont hav a book mein 10th mein hoon just passed this prob is frm a sample paper

Given taht R.F. of water is 4/3. Glass refractive index = 1.52(crown glass)

14. King

acc. to google it is 1.52

15. King

yeah and fr flint glass it is 1.62

16. King

For the fish, the apparent distance of the fly from the wall of the aquarium is µx, where µ is the R.I. of water and x is the actual distance, then apparent velocity will be . Therefore, actual velocity of fly = (8 – 3) * (3/4) = 3.75 m/s. This is the sol. given can u explain this?

Check in 10th NCERT, crown glass' R.F. is 1.52

18. King

yeah i know that i just told fr flint glas it is 1.62

19. King

so salini,ishaan,aadarsh can a ny of u explain the above sol.?

20. Ishaan94

Oh, don't consider Glass, you will have to ignore Glass, my bad :/

21. Ishaan94

btw Glass can't be ignored in real life

22. King

ok so what to do nw?

23. Ishaan94

|dw:1332858159715:dw|Apparent Velocity of fly = 8-3.

24. King

ok

25. King

why?

26. King

why ?

27. Ishaan94

because the apparent velocity is from the frame of reference in water.

28. King

ok..ok yeah....

29. King

ok 1 more..

30. King

posted!

31. salini

u have to have an idea abt relative velocity ie velocity of f fly with res[pect to velocity of fish(since both are moving) Vfly-Vfish=relative velocity of fly with respect to fish in water i think u can figure out the rest

32. salini

IN WATER CONDITION is wat i have discussed above so do the same thing in air using R.I multiply by 3/4

33. King

can u pls xplain why i hav to divide by refractive index

34. salini

wat is R.I? DID u understand the relative velocity part(it is nothing but how the fish sees the fly when it is moving)

35. King

refractive index ya i understood the r.v part

36. salini

right wat is the expression?

37. King

expression fr wat?

38. salini

refractive index of medium 1 with respect to medium 2?

39. King

idk

40. salini

it is speed of light in medium 2/speed of light in medium 1 =r.i of medium 2 use this and put the values u

41. King

@salini sry gtg can u pst solution and i shall se it tom

42. King

bye!

43. salini

thts ball u gotto work out with the expressions i gave remember it is velocity of fly in water (actual) that i gave u with relative velocity concept bye! my god this site is very slow!

44. salini

|dw:1332861296812:dw|so when u do the pproblem Vmf is only given Vmf=Vm-Vf 8=Vm-(-3) that is how it is 5m/s velocity of moth in water