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Explain the following.
$(a)$. Why is tungsten used almost exclusively for filament of electric lamps?
$(b)$. Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?
$(c)$. Why is the series arrangement not used for domestic circuits?
$(d)$. How does the resistance of a wire vary with its area of cross-section?
$(e)$. Why are copper and aluminum wires usually employed for electricity transmission?
$(a)$. Tungsten has a very high melting point which prevents the filament to burn at a very high temperature that avoids the risk of destroying the lamp. So, tungsten is used for the filament of an electric lamp.
$(b)$. In electric heating devices such as bread toasters etc., a lot of heat and temperature are required and it is a known fact that generated heat is proportional to the resistivity, and alloy offers a very high resistance rather than the pure metals. So alloys are used in electric heating devices.
$(c)$. In series-connected resistors, the potential difference is very small than the applied voltage which causes the delivered power to each device to be reduced and devices don't work efficiently. So, the series arrangement isn't used for domestic circuits.
$(d)$. We know that, $R=\frac{\rho l}{A}$
Here, $R\rightarrow$Resistance of the wire
$\rho\rightarrow$resistivity of the wire
$A\rightarrow$area of the cross-section of the wire
So, it is seen that $R\propto\frac{1}{A}$
Therefore, the resistance of a wire is inversely proportional to the area of cross-section of the wire.
$(e)$. Copper and aluminum wires have very small resistivity that makes power consumption very less as the power consumed by wire is proportional to the resistivity. So to reduce power consumption by wires during electric transmission copper and aluminum wires are used.
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