4. Charge may be measured in the following units except (a) Coulomb (b) atomic unit of charge (c) farad (d) Electromagnetic unit of charge 5. Color depends on what characteristic of light? (a) its frequency (b) its wavelength (c) both of these (d) neither of these 6. A concave mirror of radius of curvature 40 cm forms a real image twice as large as the object. What is the object distance? (a) 80 cm (b) 60 cm (c) 30 cm (d) 40 cm 7. The driving mirror of a car has a radius of curvature of 1 m. A vehicle behind the car is 4 m from the mirror. Find the image distance behind the mirror. (a) 7/8 (b) 4/9 (c) 4/7 (d) 9/2