What is the resistance of an ideal voltmeter?

Draw a schematic diagram of an electric circuit (in the "on" position) consisting of a battery of five cells of $2\, V$ each, a $5\, \Omega$ resistor, a $8\, \Omega$ resistor, a $12\, \Omega$ resistor and a plug key, all connected in series. An ammeter is put in the circuit to measure the electric current through the resistors and a voltmeter is connected so as to measure the potential difference across the $12\, \Omega$ resistor.
Calculate the reading shown by the
$(a)$ ammeter
$(b)$ voltmeter in the given electric circuit.

What is the unit of resistance?

What is the resistance of an electric arc lamp,if the lamp uses $20\, A$ when connected to a $220\, V$ line?

Which effect of electric current is used in electroplating?

Three resistors $R_{1}$,$R_{2}$,and $R_{3}$ are connected in parallel between points $A$ and $B$. The equivalent resistance $R$ is given by: