How does use of a fuse wire protect electrical appliances?

What is electrical resistivity? In a series electrical circuit comprising a resistor made up of a metallic wire, the ammeter reads $5 \mathrm{A}$. The reading of the ammeter decreases to half when the length of the wire is doubled. Why?

$B_1$, $B_2$ and $B_3$ are three identical bulbs connected as shown in figure. When all the three bulbs glow, a current of $3 \mathrm{A}$ is recorded by the ammeter $A$. What happens to the glow of the other two bulbs when the bulb $B_1$ gets fused?

$B_1$, $B_2$ and $B_3$ are three identical bulbs connected as shown in figure. When all the three bulbs glow, a current of $3 \mathrm{A}$ is recorded by the ammeter $A$. What happens to the reading of $A_1$, $A_2$, $A_3$ and $A$ when the bulb $B_2$ gets fused?

$B_1$, $B_2$ and $B_3$ are three identical bulbs connected as shown in figure. When all the three bulbs glow, a current of $3 \mathrm{A}$ is recorded by the ammeter $A$. How much power is dissipated in the circuit when all the three bulbs glow together?

Three incandescent bulbs of $100 \mathrm{W}$ each are connected in series in an electric circuit. In another circuit another set of three bulbs of the same wattage are connected in parallel to the same source. Will the bulb in the two circuits glow with the same brightness? Justify your answer.