Hi again. There's nothing worse than making mistakes and having misconceptions or in studying physics. You get nervous with your time and stop trying without any essential reason for all these. Would you like to know which mistakes I'm talking about? First one last minute study. Really bad habit for many students.

Don't study only when you have an assignment to prepare. don't study under unsuitable conditions. example, during a break at school. If you tell me about you have never done this, I won't believe you. Physics is not a point to read. One listening to hardrock second, don't try to solve a problem.

If you don't feel like you have good substantial understanding of all fundamental concepts. reviews or formulas is another bad habit but you have to live behind example I'm going to use a common one. Power is defined as work overtime. Correct? Talking about electric power in a typical direct current circuit, you may know that we use three our formulas, power equals v times I found equals i squared times R, and power equals v squared over R. A typical question which one to use? And when?

Let's try to give an answer. The first can give us the power dissipated on any electric device. The second and third of them can be applied as equivalent to the first one only when we have circuits of resistors following ohms law. Let's start with a question of is it 20 volts filament lamp and a two kilowatts electric iron work properly, both connected to a household power Supply, which of them has the bigger internal resistance? Well, this devices work properly under the same voltage, you know, 220 volts in Europe 110 volts in USA. First, we have to use the formula, the equals v squared over R. So we understand that in this case, power and resistance are inversely proportional quantities.

In other words, the biggest resistance will be this of the device which is of smallest power, and that is the final amount lamp. Can you imagine what the answer would be? If all the devices for households were connected in series instead of parallel? Just think about it. It's rather obvious. I think this example made clear what I mean when talking about wrong usual formulas.

Don't ever forget it. Thank you.