When a $12\, V$ battery is connected across an unknown resistor,there is a current of $2.5\, mA$ in the circuit. Find the value of the resistance of the resistor.

Let the resistance of an electrical component remain constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?

$A$ copper wire has a diameter of $0.5\, mm$ and a resistivity of $1.6 \times 10^{-8}\, \Omega \, m$. What will be the length of this wire to make its resistance $10\, \Omega$? How much does the resistance change if the diameter is doubled?

Judge the equivalent resistance when the following are connected in parallel: $1\, \Omega$ and $10^6\, \Omega$.

What does an electric circuit mean?

Use the data in the table to answer the following: Which material is the best conductor?

Material	Resistivity $(\Omega \,m)$
Silver	$1.6 \times 10^{-8}$
Copper	$1.62 \times 10^{-8}$
Aluminium	$2.63 \times 10^{-8}$
Tungsten	$5.20 \times 10^{-8}$
Nickel	$6.84 \times 10^{-8}$
Iron	$10.0 \times 10^{-8}$
Chromium	$12.9 \times 10^{-8}$