Success Criteria: You can solve problems involving the calculation of current and potential difference.
To continue our discussion of current, I showed you guys what an ammeter actually looks like:
On the left is an old fashion one and on the right is a modern ammeter. (Actually the one on the right is called a multimeter that can measure much more than just current.)
Handouts:
The first handout has details of the equations we would use to calculate current and potential difference.
Watch this,
Can you understand what is happening? What are the big red spheres? (Protons!) What are the little blue ones? (Electrons!)
Calculating Current
I = current, measured in units of Amperes (A)
Q = total charge, measured in units of Coulombs (C)
t = time, measured in seconds (s)
The equation is:
And for those who prefer a triangle to look at:
And for those who prefer a triangle to look at:
Q is a measure of how much charge there is. 1 C is a lot of charge! A single electron has this much charge:
It takes billions of billions of electrons to have 1 C!
Calculating Electric Potential Difference
E = energy, measured in units of Joules (J)
Q = total charge, measured in units of Coulombs (C)
∆V = electric potential difference, measured in units of Volts (V)
The equation is:
And for those who prefer a triangle, look at this:
Electric potential difference is also called "voltage" when speaking casually. It is not an easy concept to understand!
"Voltage" on it's own does not do anything, you need to have charges together with "voltage" to get any energy. I give an analogy using a roller coaster. For example, "voltage" is how high the hill is and charges are the people on the roller coaster.
A high hill by itself doesn't do anything.
You must have a cart and people on it before energy is released.
In the same way, electric potential difference (voltage) on its own doesn't do anything. You must have charges involved before any energy is released, which leads to the equation, E = Q ∆V.
More charge will give more energy. Higher potential difference will also release more energy, but they must both be present before energy is released.
Small charge and a lower potential difference will release less energy.
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| Small hill and small cart means less energy! |
Complete the first handout:
We will do the second handout together in class on Thursday.
Have fun going to work with your parents tomorrow!
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