Series vs parallel circuits

Science · Energy · ages 12-13

Name ______________________ Date ____________

Why are household circuits wired in parallel?
- To use less wire
- So each appliance gets full voltage and can be switched independently
- To reduce the total current
- To make the wiring simpler
Three resistors of 10 ohms 20 ohms and 30 ohms are connected in series. What is the total resistance?
Answer: ______________
In a parallel circuit with a battery the voltage across each branch is
- Different for each branch
- The same as the battery voltage
- Half the battery voltage
- Zero
In a parallel circuit, what is true about the voltage across each branch?
- Each branch gets a fraction of the voltage
- Each branch gets the same full voltage
- Only the branch closest to the battery gets full voltage
Why does household wiring use parallel circuits instead of series?
- So each device gets full voltage and keeps working even if another one is off
- So all devices share the exact same current
- So devices use less electricity overall
A parallel circuit has two branches. One draws 2A and the other draws 3A. What's the total current leaving the battery?
- 1A
- 6A
- 5A
A 9 V battery is connected to a 3 ohm and a 6 ohm resistor in series. What is the current in the circuit?
Answer: ______________
A series circuit has a 10V battery and two bulbs. Bulb A drops 4V. How many volts does Bulb B drop?
Answer: ______________
A student wires three bulbs in series and says: 'If one bulb burns out, the others should stay lit since they're not touching the broken one.' What's wrong with this reasoning?
- Nothing is wrong, the student is correct
- Series circuits have only one path, so a broken bulb breaks the whole loop and everything goes out
- The other bulbs would just get brighter instead
A room in your house doesn't go dark when one lamp is switched off, but an old string of Christmas lights goes dark if one bulb breaks. A friend says this is because house bulbs are 'stronger.' What's the real reason?
- House bulbs are made of tougher glass
- Christmas lights use less electricity so they break more easily
- House circuits are wired in parallel, so each light has its own path to the power source

Answer key

For grown-ups. Fold this page away before handing over the rest.

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So each appliance gets full voltage and can be switched independently · Parallel wiring gives each outlet full voltage. Appliances can be turned on and off independently without affecting others.
60 · In series resistances add: 10 + 20 + 30 = 60 ohms.
The same as the battery voltage · In parallel all branches connect directly across the battery terminals so they all have the same voltage.
Each branch gets the same full voltage · Every branch connects straight across the battery, so each one sees the same full voltage.
So each device gets full voltage and keeps working even if another one is off · Parallel wiring gives each device its own path to the full voltage, so switching one off doesn't affect the rest.
5A · Parallel branch currents add up: 2A plus 3A equals 5A.
1 · Total R = 3 + 6 = 9 ohms. I = V/R = 9/9 = 1 A.
6 · Series voltages add up to the total: 10V minus the 4V already used by Bulb A leaves 6V.
Series circuits have only one path, so a broken bulb breaks the whole loop and everything goes out · In series, every part shares the same single path. Break it anywhere and current stops flowing everywhere in that loop.
House circuits are wired in parallel, so each light has its own path to the power source · It comes down to wiring, not bulb strength. Parallel branches keep working independently, while a broken series loop kills the whole string.