Question

descibe the mirror formula class 10

Answer 1

mirror formula
1/f=1/v+1/u
and lens formula
1/f= 1/v-1/u
where f= focal length
v= image distance
u= object distance
both formula have difference of sign so don't confuse Thanks

Answer 2

Hey mate
Mirror formula is the relationship between object distance (u), image distance (v) and focal length.

1v+1u=1f1v+1u=1f

proof of mirror formula:



In ΔABCΔABC and ΔA′B′C′ΔA′B′C′

ΔABCΔABC ∼∼ ΔA′B′CΔA′B′C [AA similarity]

ABA′B′=ACA′C′ABA′B′=ACA′C′ ⋯⋯(1)

Similarly, In ΔFPEΔFPEand ΔA′B′F′ΔA′B′F′

EPA′B′=PFA′FEPA′B′=PFA′F

ABA′B′=PFA′FABA′B′=PFA′F [ AB=EP] ⋯⋯(II)

From (i) &(ii)

ACA′C=PFA′FACA′C=PFA′F

=>A′CAC=A′FPF=>A′CAC=A′FPF

=>(CP−A′P)(AP−CP)=(A′P–PF)/PF=>(CP−A′P)(AP−CP)=(A′P–PF)/PF

Now, PF=−f;CP=2PF=−2fPF=−f;CP=2PF=−2f ; AP=−uAP=−u ; and A′P=−vA′P=−v

Put these value in above relation:

⟹[(−2f)–(−v)](−u)−(−2f)=[(−v)–(−f)](−f)⟹[(−2f)–(−v)](−u)−(−2f)=[(−v)–(−f)](−f)

⟹uv=fv+uf⟹uv=fv+uf

⟹1f=1u+1v