What are the units of resistance?

How are ammeters and voltmeters connected in a circuit? What do they help us measure?

When two resistors of resistances $R_{1}$ and $R_{2}$ are connected in parallel,the net resistance is $3 \, \Omega$. When connected in series,its value is $16 \, \Omega$. Calculate the values of $R_{1}$ and $R_{2}$.

State which has a higher resistance,a $50 \, W$ or a $25 \, W$ lamp bulb,and by how many times?

Two students perform experiments on series and parallel combinations of two given resistors $R_{1}$ and $R_{2}$ and plot the following $V-I$ and $I-V$ graphs. Which of the graphs is (are) correctly labelled in terms of the words 'series' and 'parallel'? Justify your answer.

What is the cause of resistance?