Which two features both affect the sensitivity of the thermometer?

Here are the solutions to the questions:

Question 19:

• Concept: Pressure is defined as force per unit area ($P = \frac{F}{A}$). When a student pushes a pin, the force applied by the thumb on the pin head is equal to the force exerted by the pin tip on the notice board (Newton's third law). However, the area of the pin tip is much smaller than the area of the pin head. Therefore, the pressure at the pin tip is much greater than the pressure on the thumb. This high pressure at the tip allows it to penetrate the board, while the lower pressure on the thumb prevents it from being penetrated.

• Step 1: Identify the forces involved. The force exerted by the thumb on the pin is equal to the force exerted by the pin on the notice board.

• Step 2: Compare the areas. The area of the pin tip (on the notice board) is much smaller than the area of the pin head (on the thumb).

• Step 3: Apply the pressure formula. Since pressure is inversely proportional to area for a constant force, the pressure on the notice board (small area) is greater than the pressure on the thumb (large area).

The correct statement is:
D) The pressure of the pin on the notice board is greater than the pressure of the pin on her thumb.

Question 20:

• Concept: The sensitivity of a liquid-in-glass thermometer refers to how much the liquid column rises for a small change in temperature.

  • A larger volume of liquid in the bulb means a greater expansion for a given temperature rise, leading to a more noticeable change.
  • A narrower bore (smaller diameter of the liquid thread) means that for the same volume expansion, the liquid will rise higher in the capillary tube, making the thermometer more sensitive.

• Step 1: Consider the effect of the amount of liquid. A larger mass (and thus volume) of liquid in the bulb will expand more for a given temperature change, increasing sensitivity.

• Step 2: Consider the effect of the liquid thread's diameter. A smaller diameter of the capillary tube (liquid thread) means that the same volume expansion will cause the liquid to rise a greater distance, increasing sensitivity.

• Step 3: Evaluate the options based on these factors.

The two features that both affect the sensitivity of the thermometer are:
A) mass of liquid and diameter of liquid thread