What are the factors on which heat dissipated by a conductor depends?

$(a)$ $A$ Nichrome wire of length $L$ and radius $r$ has a resistance of $10 \, \Omega$. How would the resistance of the wire change when:
$(i)$ only the length of the wire is doubled?
$(ii)$ only the diameter of the wire is doubled? Justify your answer.
$(b)$ Why are the elements of electrical heating devices made up of alloys?

There is a frill of $20$ bulbs connected in series in a room. One bulb gets fused. The remaining $19$ are again joined in series and connected to the same supply. Will the light increase or decrease in the room?

Why are alloys commonly used in electrical heating devices?

$100 \, J$ of heat is produced each second in a $4 \, \Omega$ resistance. Find the potential difference across the resistor. (in $, V$)

Five bulbs are connected in a parallel circuit. If the second bulb blows out,what happens?