Question

Identify the instrument from the diagram given below.

• A. Potometer
• B. Arc auxanometer
• C. Lever auxanometer
• D. potentiometer

Answer 1

The correct option is B Arc auxanometer

The instrument in the image is an arc auxanometer.

Arc auxanometer consists of a pulley attached to a pointer or needle with unequal arms. The long arm can move over a graduated arc and the short arm consists of an adjustable large screw. This helps in adjustment of the weight of the pointer so that the long arm can move freely over the arc upside downwards.

It basically magnifies the growth of the plant. The magnification is equal to the length of the long arm as measured from the centre of the pulley, divided by the radius of the pulley.

Unspun silken thread is tied to the stem tip of the plant, the shoot growth of which is to be measured. The other end of the thread is tied to a small weight.

The thread is passed over the pulley so that the small weight hangs down freely. The small weight keeps the thread stretched.

It additionally helps the pulley to move along with its movement. As the stem grows in length, the small weight moves downwards. The pulley and the pointer move too. The distance through which the pointer moves is read on the graduated arc and the growth is measured.