First slide

Heat ;work and internal energy

Question

How many calories of heat is developed by 200 watt bulb in 5 minutes?

Moderate

A

$1.43 \times 10^{3} c a l s$
B

$1.43 \times 10^{4} c a l s$
C

$14.3 \times 10^{3} c a l s$
D

$14.3 \times 10^{4} c a l s$

Solution

$\begin{array}{rcl} P o w e r & = & \frac{E n e r g y}{t i m e} \\ \Rightarrow & E n e r g y = P o w e r x t i m e i n s e c o n d s \\ g i v e n P o w e r & = & 200 W \\ t i m e & = & 5 \times 60 = 300 s \\ s u b s t i t u t e t h e g i v e n v a l u e s i n E n e r g y e q u a t i o n \\ t o t a l e n e r g y & = & 200 \times 5 \times 60 = 6 \times 10^{4} J \\ 4.2 J & = & 1 c a l o r i e (c o n v e r s i o n) \\ 1 J & = & \frac{1}{4.2} c a l o r i e \\ t o t a l h e a t e n e r g y d e v e l o p e d & = & \frac{6 \times 10^{4}}{4.2} c a l = \frac{10}{7} \times 10^{4} c a l \\ t o t a l h e a t e n e r g y d e v e l o p e d & = & 1.43 \times 10^{4} c a l \end{array} \begin{array}{rcl} \end{array}$

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