Series & Parallel Circuits (AQA GCSE Physics): Revision Notes
AC and DC
Electric circuits can work using two different types of electrical supply. These are called alternating current and direct current.
What is direct current?
Direct current (dc) is when electric current flows in just one direction through a circuit. The electrons always move the same way around the circuit.
Where do we get dc from?
- Cells and batteries provide direct current
- The electrons flow from one terminal to the other in a steady stream
- You need a complete circuit for the electrons to flow properly
When you connect a battery to an oscilloscope, you see a straight horizontal line. This shows that the voltage stays constant and doesn't change over time.
Oscilloscope Display for DC:
A battery might give a steady 2.8V, which appears as a flat horizontal line on the oscilloscope screen, indicating no variation in voltage over time.
What is alternating current?
Alternating current (ac) works very differently from direct current. With ac, the electric current keeps changing direction back and forth.
Key facts about ac:
- The current flows one way, then switches and flows the other way
- This switching happens very regularly
- The voltage also changes constantly - it goes up and down
AC current shows up as a wavy line that goes up and down on an oscilloscope. This wave pattern is called a sine wave. It shows how the current and voltage keep changing direction.
UK Mains Electricity Details:
- UK mains electricity is ac
- It has an average voltage of 230V
- The frequency is 50Hz (this means 50 cycles per second)
- Because the current changes direction twice in each cycle, it actually switches direction 100 times every second!
Using dc and ac in the home
Both types of current are useful in our homes for different jobs.
Never connect DC devices directly to AC mains supply or vice versa!
Most devices are designed for either AC or DC specifically. Using the wrong type of supply can damage equipment or be dangerous.
Direct current uses:
- Supplied by cells and batteries
- Powers portable devices
- Used in some electronic equipment
Alternating current uses:
- Comes from the mains supply (wall sockets)
- Powers most household appliances
- Transfers energy to motors and heating devices
The power rating tells you how much energy an appliance uses each second. Different electrical appliances need different amounts of power.
Typical Power Ratings for Home Appliances:
- Electric kettle: 2200W
- Hair dryer: 1500W
- Microwave: 850W
- Electric oven: 3000W
- Electric shaver: 15W
The higher the power rating, the more electricity the appliance uses.
Understanding these differences helps you choose the right type of electrical supply for different devices and understand your home's energy consumption.
Key Points to Remember:
- DC flows in one direction - like a river flowing downstream
- AC changes direction regularly - like waves going back and forth
- Batteries give DC, mains supply gives AC
- UK mains is 230V at 50Hz - changing direction 100 times per second
- Power ratings tell you how much energy appliances use each second