to-the-left-of-the-mirror-on-their-page-what-is-the-best-evaluation-of-this-step

Question

A student solving 1do+1di=1f\displaystyle\frac{1}{d_{o}}+\frac{1}{d_{i}}=\frac{1}{f} for a concave mirror with a real object substitutes do=−25d_{o}=-25 cm because the object is to the left of the mirror on their page. What is the best evaluation of this step?

Accepted Answer

It is incorrect because object distance is positive when the object is on the same side as the incoming light

Answer

It is incorrect only because the image distance should be assigned a sign before the equation is solved

Answer

It is correct only if the focal length is also made negative for a concave mirror

Answer

It is correct because left of the mirror is always negative by the sign convention

A student solving 1do+1di=1f\(\displaystyle\)\(\frac{1}{d_{o}\)}+\(\frac{1}{d_{i}\)}=\(\frac{1}{f}\) for a concave mirror with a real object substitutes do=−25d_{o}=-25 cm because the object is to the left of the mirror on their page. What is the best evaluation of this step?

A student solving $\frac{1}{d_{o}} + \frac{1}{d_{i}} = \frac{1}{f}$ for a concave mirror with a real object substitutes $d_{o} = - 25$ cm because the object is to the left of the mirror on their page. What is the best evaluation of this step?