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Potential difference can be measured by connecting a voltmeter in parallel between two points in a circuit
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The energy transferred per unit charge flowing from one point to another
Potential difference can be measured by connecting a voltmeter in parallel between two points in a circuit
Calculate the work done in moving a charge of 5 C through a potential difference of 20 V.
Step 1: Write down the known quantities
Step 2: Write down the relevant equation
Step 3: Rearrange for the work done, W
W = VQ
Step 4: Substitute in the values
W = 20 × 5 = 100 J
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In metals, the current is caused by a flow of electrons
Calculate the current through a lamp when a charge of 4 C passes through it in 500 s.
Step 1: Write down the known quantities
Step 2: Write down the relevant equation
Q = It
Step 3: Rearrange for current, I
Step 4: Substitute in the values
Students often confuse charge and current. When we say charge in terms of electrical circuits, we are really talking about a quantity of electrons. A unit of charge, one coulomb (1 C) is 6.24 × 1018 electrons. When delocalised electrons flow around a circuit, the amount of charge passing a fixed point (like an ammeter) per second is the current. So an ammeter is basically counting the number of electrons or the amount of charge flowing through it each second. One amp (1 A) of current is one coulomb of charge per second (1 C / s).
By definition, conventional current always goes from positive to negative (even through electrons go the other way)
An ammeter can be used to measure the current around a circuit and always connected in series
The current is the same at each point in a closed-loop
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