When an object is placed at a distance of $25 \; cm$ from a mirror,the magnification is $m_1$. The object is moved $15 \; cm$ away with respect to the earlier position,magnification becomes $m_2$. If $\frac{m_1}{m_2} = 4$,the focal length of the mirror is: (in $; cm$)

The focal length of a concave mirror is $50 \, cm$. Where should an object be placed so that its image is two times magnified and inverted?

In an experiment to determine the focal length $(f)$ of a concave mirror by the $u-v$ method,a student places the object pin $A$ on the principal axis at a distance $x$ from the pole $P$. The student looks at the pin and its inverted image from a distance keeping his/her eye in line with $PA$. When the student shifts his/her eye towards left,the image appears to the right of the object pin. Then,

$A$ convex mirror is used to form the image of an object. Then which of the following statements is wrong?

In an experiment to find the focal length of a concave mirror,a graph is drawn between the magnitudes of $u$ and $v$. The graph looks like:

The focal length of a convex mirror is $20\, cm$. Its radius of curvature will be.....$cm$.