What is the best position for eye viewing an object through microscope ?

A student measures the thickness of a human hair by looking at it through a microscope of magnification 100. He makes 20 observations and finds that the average width of the hair in the field of view of the microscope is 3.5 mm. What is the estimate on the thickness of hair?

What is the function of iris and pupil in human eye?

What is principle of super position?

What is the work done when the force on the object is zero?

What is the fundamental difference between a microscope and a telescope?

What is the direction of force of friction acting on a moving object?

A force of 7 N acts on an object. The displacement it, say 8m, in the direction of the force. Let us take it that the force acts on the object through the displacement. What is the work done in this case?