How current, potential difference and resistance behave in each type of circuit, why adding parallel resistors lowers total resistance, and how to work through circuit questions.
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1.What is a series circuit?
One where the components are connected one after another in a single loop, so there is only one path for the current.
2.What is a parallel circuit?
One where the components are connected on separate branches, so the current has more than one path.
3.What happens to current in a series circuit?
It is the same at every point in the circuit.
4.What happens to potential difference in a series circuit?
The potential differences across the components add up to the potential difference of the supply.
5.What happens to resistance in a series circuit?
The total resistance is the sum of the individual resistances.
6.Two resistors of 4 and 6 ohms are in series. What is the total resistance?
4 + 6 = 10 ohms.
7.What happens to current in a parallel circuit?
The total current from the supply is the sum of the currents in each branch.
8.What happens to potential difference in a parallel circuit?
It is the same across each branch, and equal to the supply potential difference.
9.What happens to total resistance when resistors are added in parallel?
The total resistance decreases.
10.Why does adding a parallel resistor decrease total resistance?
It provides an extra path for the current, so more current flows in total for the same potential difference.
11.How does the total resistance of two parallel resistors compare with the smallest one?
It is always less than the resistance of the smallest individual resistor.
12.Two identical 10 ohm resistors are in parallel. What is the total resistance?
5 ohms, half the value of one of them.
13.Why do two lamps in series look dimmer than one on its own?
The total resistance is higher so the current is smaller, and the supply potential difference is shared between them.
14.Why do lamps in parallel stay at full brightness?
Each has the full supply potential difference across it, regardless of the other branches.
15.What happens if one lamp breaks in a series circuit?
The circuit is broken, so no current flows and all the components stop working.
16.What happens if one lamp breaks in a parallel circuit?
Only that branch stops working. The others continue as normal.
17.Why is household wiring in parallel?
So each appliance gets the full mains potential difference and can be switched on and off independently.
18.A 12 V supply is across two equal series resistors. What is the potential difference across each?
6 V each, since the supply is shared equally between identical resistors.
19.A 12 V supply is across two parallel branches. What is the potential difference across each?
12 V across each branch.
20.In series with 3 ohm and 6 ohm resistors and a 9 V supply, what is the current?
Total resistance is 9 ohms, so current = 9 divided by 9 = 1 A.
21.Using that circuit, what is the potential difference across the 6 ohm resistor?
1 x 6 = 6 V.
22.Where should a switch be placed to control the whole circuit?
In the main branch in series with the supply, so opening it breaks every path.
23.How does adding a cell in series affect the current?
It increases the total potential difference, so the current increases.
24.Why does the current split unevenly between unequal parallel branches?
The branch with lower resistance carries more current, since they have the same potential difference across them.
25.What is the first step in solving most circuit problems?
Work out the total resistance, then use the supply potential difference to find the total current.
26.Why can potential difference be measured across a whole series combination?
The potential differences add, so measuring across both gives the total, which equals the supply.
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