Question

The inner and outer surfaces of a 0.5-cm-thick 2-m 2-m window glass in winter are 10c and 3c, respectively. If the thermal conductivity of the glass is 0.78 w/m c, determine the amount of heat loss, in kj, through the glass over a period of 5 hours

Answer 1

Volume of hollow cylinder == Volume of solid cylinder

\Rightarrow \pi \left( { R }_{ 2 }^{ 2 }-{ R }_{ 1 }^{ 2 } \right) H=\pi { r }^{ 2 }h\Rightarrow \left( { 20 }^{ 2 }-{ 15 }^{ 2 } \right) \times h={ r }^{ 2 }h\quad \left[ \because \quad height\quad is\quad same \right]⇒π(R

2

2

−R

1

2

)H=πr

2

h⇒(20

2

−15

2

)×h=r

2

h[∵heightissame]

\Rightarrow r=\sqrt { 175 } =13.2cm⇒r=

175

=13.2cm

\therefore∴ Radius of solid cylinder is 13.2cm.13.2cm.