Electrical Circuits P2

What are the two types of current electricity?

Direct current (DC) and alternating current (AC)

What is direct current (DC)?

Current that flows in one direction only.

What is DC typically associated with?

Battery-powered circuits.

What does a DC current-time graph look like if the current is constant?

A horizontal line because the current remains in the same direction and at a constant level.

What is alternating current (AC)?

Current that oscillates from one direction to the other.

What is AC typically associated with?

Mains electricity circuits

What does an AC current-time graph show?

A waveform that repeatedly changes direction, passing between positive and negative current.

What is a cycle in AC electricity?

One complete oscillation from zero, through positive current, back to zero, through negative current, and back to zero.

What happens after one AC cycle?

The cycle repeats.

What is the unit of frequency?

Hertz (Hz).

What does 1 Hz mean?

One cycle per second.

What does frequency tell you about an AC supply?

How many complete cycles occur per second.

If an AC supply completes 50 cycles per second, what is its frequency?

50 Hz.

What is the mains electricity voltage in Ireland?

230 V.

What is the frequency of mains electricity in Ireland?

50 Hz.

What does 50 Hz mean for Irish mains electricity?

The current oscillates through 50 complete cycles every second

What range of voltage does European mains electricity vary around?

Approximately 220–240 V.

What tolerance around 230 V is given in the lecture?

±10%.

Does mains electricity have the same voltage and frequency everywhere?

No. For example, some countries use approximately 110/120 V and 60 Hz.

What does a battery provide in a circuit?

Potential difference/potential.

What does a DC supply provide?

Potential

What is the function of a fuse?

It acts as a safety device.

What does an AC supply provide?

Potential

What does a capacitor do?

Stores charge.

What does an inductor do according to the lecture?

Stores charge.

What does a transformer do?

Converts potential.

What does the ground symbol represent?

An earth potential point.

Label

What is electrical power?

The amount of electrical energy being used or transferred per unit time.

What is the unit of power?

Watt (W).

What does 1 watt mean?

1 ampere flowing through a potential difference of 1 volt.

What is the main formula for electrical power?

P = IV

What is Ohm’s law?

V = IR

What is the power formula in terms of current and resistance?

P = I²R

How can P = I²R be derived?

Start with P = IV and substitute V = IR:
P = I(IR) = I²R

What power formula should you use if you know current and voltage?

P = IV

What power formula should you use if you know current and resistance?

P = I²R

What is the power dissipated by a resistor?

The electrical power converted into other forms of energy, such as heat, by the resistor.

When calculating the power of a resistor in a parallel branch using P = I²R, which current should you use?

The current through that particular resistor, not the total circuit current.

What is a kilowatt-hour (kWh)?

The energy consumed by using 1 kW of power for 1 hour.

What unit do electricity companies charge customers for?

Kilowatt-hours (kWh).

What formula is used to calculate electrical energy consumption in kWh?

Energy (kWh) = Power (kW) × Time (h)

How do you convert watts to kilowatts?

Divide by 1000.

How do you calculate the cost of electricity?

Cost = Energy consumed (kWh) × price per kWh

How do you calculate the cost of electricity at different tariffs?

Calculate the energy consumption in kWh, then multiply it by the relevant price per kWh.

What happens to the potential difference of batteries connected in series?

Their potentials/voltages add together.

What happens when identical batteries are connected in parallel?

Their voltage does not increase, but they can supply current for longer.

What is important when connecting batteries in parallel?

They should have equal potential/voltage.

What is the total resistance of resistors in series?

RT = R₁ + R₂ + R₃ + …

What is the formula for resistors in parallel?

1/RT = 1/R₁ + 1/R₂ + 1/R₃ + …

What is the first step when solving a mixed resistor circuit?

Simplify the parallel resistors into a single equivalent resistor.

What is the second step?

Simplify the circuit into one total resistance.

What is the third step?

Calculate the total current.

What is the fourth step?

Calculate the voltage drop across each stage, starting with series resistors.

What do you do when current splits between parallel branches?

Use I = V/R to calculate the current through each resistor.

What is the important rule when calculating power in a parallel resistor?

Use the current through that individual resistor, not the total current, in P = I²R

Good calculation