When an object is placed \( 40 \, \text{cm} \) away from a spherical mirror an image of magnification \( \dfrac{1}{2} \) is produced. To obtain an image with magnification of \( \dfrac{1}{3} \), the object is to be moved:
\( 40 \, \text{cm} \) away from the mirror
\( 20 \, \text{cm} \) towards the mirror
\( 80 \, \text{cm} \) away from the mirror
\( 20 \, \text{cm} \) away from the mirror