A ray from a fixed object is incident on a plane mirror at an angle of 20^o. If the mirror is rotated through 30^o by how many degree would the reflected ray rotate?

Which of the following distances is usually adjustable in the camera? The distance between the

A travelling microscope is focused on a mark on a table. If a glass block of thickness 18.0cm is placed on the mark by how many centimeters will the microscope be moved upwards so as to focus the mark once again? [refractive index of glass = 1.5]

In which of the following media would sound wave travel fastest?

Which of the following actions is necessary in order to tune a string to produce a note of an octave higher than its fundamental?