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WAEC Physics 2019 Paper

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Question : 36

Total: 49

A rectangular piece of iron measuring 4 cm by 3 cm at 20

^{\circ}

C is heated until its temperature increases by 100 C. Calculate the new area of the metal. [Linear expansivity of iron is 1.2x 10

^{-5}

^{-1}

]

12.0144 cm $^{3}$
12.0346 cm $^{3}$
12.0288 cm $^{3}$
12.0173 cm $^{3}$

Solution:

Linear expansivity ( $\alpha$ )

= $\frac{\;A_2\; - \;A_1}{A_1\theta}$

Original Area(A $_{1}$ ) = 4 x 3 = 12

New Area (A $_{2}$ ) = ?

Temp. rise ( $\theta$ ) = 100 $^{\circ}$ C

A $_{2}$ - 12 = 1200 x 2 x 1.2 x 10 $^{-5}$

A $_{2}$ - 12 = 2880 x 10 $^{-5}$

A $_{2}$ - 12 = 0.0288

A $_{2}$ = 12.0288 cm $^{2}$

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