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 Is the bulb of a thermometer made of diathermic or adiabatic wall?

Diathermic walls are used in the bulb of thermometer as they allow to conduct heat through it into mercury of bulb, whereas adiabatic walls does not allow to pass heat through it.

A student records the initial length l, change in temperature \Delta T and change in length \Delta l of a rod as follows:

S.No

l (m)

\Delta T (^{\circ}C)

\Delta l (m)

1

2

10

4 \times 10^{-4}

2

1

10

4 \times 10^{-4}

3

2

20

2 \times 10^{-4}

4

3

10

6 \times 10^{-4}

If the first observation is correct, what can you say about observations 2, 3, and 4.

Answers (1)

Here, it is given that there  is a rod and a material that has linear expansion ‘\alpha’, remains same.

\Delta t is same here.

Now, from observation no. 1

\alpha =\frac{\Delta L}{L \Delta t}

   \alpha=\frac{4 \times 10^{-4}}{2 \times 10}= 2 \times 10^{-5} /C^0

Now, for observation no. 2,

\Delta L=\alpha L \Delta t

    = 2 \times 10^{-5} \times 1 \times 10

    = 2 \times 10^{-4}m viz. not equal to 4 \times 10^{-4}m

Now, for observation no. 3,

\Delta L=\alpha L \Delta t
   = 2 \times 10^{-5} \times 2 \times 20

   = 8 \times 10^{-4} viz. not equal to = 2 \times 10^{-4}m

Now, for the last observation, i.e., no. 4,

\Delta L=\alpha L \Delta t

  = 2 \times 10^{-5} \times 3 \times 10

    = 6 \times 10^{-4 }= 6 \times 10^{-4}m.

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