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3 years ago

Hello I need the formula for getting the focal length of a concave mirror

2 answers:

7 0

The focal length of a concave mirror is negative and that of a convex mirror is positive. You can also prove the same by using the mirror formula (1/f = 1/v +1/u).

Let's see how,

Since we know object is always placed on the left side or direction opposite to the incidence ray of the mirror. Therefore object distance will always be negative.

u = -u

v = -v (Image distance is negative, since image formed by concave mirrors are generally on the left side or direction opposite to the incidence ray)

Using mirror formula,

1/f = 1/v +1/u

or, 1/f = (-u-v)/uv

or, f = -uv/(u+v)

As you can see, The value of f is negative here…

However v is not always negative in concave mirror, when object is placed between focus and pole, you will get a virtual image on the right side of the mirror, so in this case image distance will be positive. But even in this case focal length will be negative. How?

Just use the mirror formula again, and you will know how.

mars1129 [50]3 years ago

6 0

Answer:

f= -9cm, v= -6cm. The focal length of a concave mirror can be estimated by focusing a distant object on a screen. Parallel rays from a distant object converge at the focal plane of the mirror. The distance between the mirror and the screen is the estimated focal length of the concave mirror.

Explanation:

Hope this help!

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Answer:

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Explanation:

Look at the attached graphic

we take the forces acting on the x-y plane and applied at the origin of coordinates

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Calculation of the components of equilibrant force (Fe)

the x-y components of the equilibrant force are equal in magnitude but in the opposite direction to the net force components:

Fnx= -2341.87 P, then, Fex= +2341.87 P

Fny= -1081.87 P P, then, Fex= +1081.87 P

Magnitude of the equilibrant (Fe)

$F_{n} = \sqrt{(F_{nx})^{2} +(F_{ny})^{2} }$

$F_{e} =\sqrt{(2341.87)^{2}+(1081.87)^{2} }$

Fe= 2579.68 P

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$\alpha =tan^{-1} (\frac{F_{ny} }{F_{nx} } )$

$\alpha =tan^{-1} (\frac{1081.87 }{2341.87} )$

α= 24.8°

Look at the attached graphic

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