Question
Question: Centigrade and Fahrenheit thermometers are dipped in boiling water and the water temperature is lowe...
Centigrade and Fahrenheit thermometers are dipped in boiling water and the water temperature is lowered until the Fahrenheit thermometer registers 140. The fall in temperature as registered by the centigrade thermometer is........ .
A) 30∘
B) 40∘
C) 60∘
D) 80∘
Solution
We know the relation between the centigrade and Fahrenheit scale so we can use that relation in this question.
We know the centigrade scale have 100∘c as the boiling point of water and in Fahrenheit scale 212∘F
Step by step solution:
We know that in centigrade scale freezing point of water is 0∘c and boiling point 100∘c and it divide into 100 equal parts
And in Fahrenheit scale it start from 32∘F to 212∘F and divided into 180 equal parts
So we can write
⇒100ΔTc=180ΔTF
This is the relation between centigrade and Fahrenheit scale
Here temperature fall down in Fahrenheit scale 212 to 140 so ΔTF=212−140
Put in above equation
⇒100ΔTc=180212−140
⇒ΔTc=18072×100
Solving this we get a fall down in centigrade scale.
∴ΔTc=40∘
Hence option B is correct
Note:
We can solve this question by another method we know 5c=180F−32
Put F=140 c=(180140−32)×5
Solving this we get c=60∘
Since the temperature of boiling water is 100∘c so the require fall is 100−60=40∘c