Question

Hello!

please can anyone help me with these questions:


1) An object is 20 cm from a concave mirror of focal length 40 cm. Calculate the distance from the image to the mirror.

2) An object is 40 cm from a concave mirror and the image is formed 60 cm from the mirror. Calculate the magnification.

3) An object is 40 cm from a convex mirror and the image is formed 20 cm from the mirror. Calculate the focal length of the mirror.

4) An object is placed 30 cm in front of a concave mirror. A real image of the object is formed 50 cm from the mirror. What is the focal length of the mirror? if the object is 5 cm high what is the height of the image?


thank you :)

Answer 1

yes
1)u=-20cm,f=-40cm
v=(uf)(u-f)
v=(-20*-40)(-20-(-40))
v=800/20=40cm

2)m=-v/u
since u have not specified whether the image is real or virtual.
2 cases r possible
i)image is real then v=-60,u=-40
=>m=-60/40=-1.5
ii>image is virtual
v=60,u=-40
=>m=60/40=1.5

3)in a convex mirror image is always virtual so v=20cm,u=-40cm
f=uv/(u+v)
f=(-800)/(-20)=40cm

4)u=-30cm,v=-50cm
f=(uv)/(u+v)
f=1500/-80=(-18.75cm)
h1=5cm
h2=?
h2=(-v*h1)/u
h2=(50*4)/-30=-200/30=-20/3=-6.67cm

hope it helps.. but don't give such question for just 5 points