Johns face is 20 cm in front of a concaveshaving mirror of focal length 30 cm. How large an image doeshe observe? A) twice as large as his face B) half as large as his face C) four times as large as his face D) of the same size as his face E) three times as large as his face Why? Johns face is 20 cm in front of a concaveshaving mirror of focal length 30 cm. How large an image doeshe observe? A) twice as large as his face B) half as large as his face C) four times as large as his face D) of the same size as his face E) three times as large as his face Why?
Explanation / Answer
given the focal lengh is f = 30 cm the object distance is p =20 cm the image is virtual so 1/f = 1/P + 1/q solving this q = -60 cm magnification is m = - q / P = 3 three times as large as his face