When the current through an ohmic conductor is 2A, the potential difference across it is 6V. What is the potential difference across the same ohmic conductor when the current is increased to 3A?

To answer this, you need to pick up on the clues in the question. "Ohmic conductor" is explicitly mentioned twice, so this is likely to be important. You should know that for ohmic conductors, p.d. is proportional to current, which means p.d./current=constant (called the constant of proportionality). You can calculate the constant from the first part of the question, 6/2=3.Now you know the constant, rearrange the equation to make what you want to find out, the p.d., the subject:p.d.=constantcurrentNow, you can use this equation and put in the numbers you know: p.d.=33=9V (don't forget the units!)If you'd prefer, you can also solve this using a graph. Draw a straight-line graph that cuts through zero-zero, with p.d. on the y-axis and current on the x-axis. The constant of proportionality is the gradient of the line, and can be found by finding difference in two y values (6-0) and dividing by difference in two x values (2-0). You can then use the equation above to find the p.d. in the second scenario, and you should get the same answer, 9V.