17. A concave mirror produces a real image 10mm tall, of an object 2.5mm tall placed at 5cm from the mirror. Calculate focal length of the mirror and the position of the image. 18. An object is placed at a large distance in front of a convex mirror of radius of curvature 40cm. How far is the image behind the mirror? 19. An object is placed 15cm from a convex mirror of radius of curvature 90cm. Calculate position of the image and its magnification. 20. The image formed by a convex mirror of focal length 30cm is a quarter of the object. What is the distance of the object from the mirror? 21. When an object is placed at a distance of 60cm from a convex mirror, the magnification produced is 1/2. Where should the object be place to get a magnification of 1/3? 22. An object is placed 18cm front of a mirror. If the image is formed at 4cm to the right of the mirror. Calculate its focal length. Is the mirror convex or concave? What is the nature of the image? What is the radius of curvature of the mirror?