# phy mc qs.......

2. The lengths of mercury thread in the uniform tube above the bulb of a mercury thermometer are:

30mm when the bulb is melting ice; 180mm when the bulb is in the steam above boiling water; 12mm when the bulb is in a liquid, what is the temperature of the liquid?

A.-8oC

B.-12 oC

C.6.7 oC

D.8.0 oC

### 2 個解答

• 1 十年前
最愛解答

Length of mercury thread changes in direct proportion to the liquid temperature.

Melting Ice = 0 deg C

Steam = 100 deg C

Let y be the temperature of the liquid:

(y-0)/(100-0)= (12-30)/(180-30)

therefore y = -12 deg C or Answer is B

• 1 十年前

By the fact that the expansion of mercury is linear with temperature, we have:

Length of mercury thread at 0°C = 30 mm

Length of mercury thread at 100°C = 180 mm

So the temperature θ (in °C), for a given length of thread L, are related by:

L = 30 + θ × (180 - 30)/100

So when L = 12, we have:

12 = 30 + θ × 150/100

θ = -12

Hence the temperature is -12°C.