Chapter 2 - Circuit Concepts

What is the standard way to draw, communicate and analyse circuits?

Use standard circuit symbols and convention

Name ways to measure voltage, current and resistance in circuits.

Use a multimeter, voltmeter, ammeter, logic probe, oscilloscope

What is the formula for voltage in terms of current and resistance?

V = I × R

What is the formula for power in terms of voltage and current?

P = V × I

What is the formula for power using current and resistance?

P = I² × R

What is the formula for power using voltage and resistance?

P = V² ÷ R

What formula links energy, power and time?

E = P × t

What is a circuit diagram?

A representation of an electrical circuit using symbols for each component

Name three components drawn with specific circuit symbols.

Lamp, resistor, battery

What is a cell?

A single electrochemical source of voltage

What is a battery?

Two or more cells connected in series

What is the symbol for a variable resistor?

Resistor symbol with a diagonal arrow

What is the unit for current?

Ampere (A)

How is current measured?

With an ammeter in series with the circuit

What is an electron?

Negatively charged particle in an atom; flows in a circuit as current

What is the difference between a conductor and insulator?

Conductors (e.g. copper) have free electrons; insulators (e.g. PVC) do not

How does conventional current flow?

From the positive to the negative terminal

How does electron flow differ from conventional current?

It moves from negative to positive terminal

What is the current through all components in a series circuit?

The same everywhere in the circuit

What is the rule for currents at a junction in a parallel circuit?

Current splits between branches and total in = total out

How do you convert amperes to milliamperes?

Multiply by 1000

How do you convert amperes to microamperes?

Multiply by 1,000,000

How do you convert milliamperes to amperes?

Divide by 1000

If 3A pass through a circuit, how many mA is this?

3000mA

What happens to current if a lamp in a series circuit blows?

No current flow anywhere in the circuit, all lamps go out

What happens if one lamp fails in a parallel circuit?

Current still flows in other branches, other lamps stay on

What does an ammeter measure?

Electric current in amperes (A)

Where should you place an ammeter?

In series with the circuit element you wish to measure

What is the purpose of a multimeter?

Measure multiple values (current, voltage, resistance) in one device

What is the advantage of a digital multimeter?

Easy, direct reading; shows minus if connected backward—not damaged

How does a multimeter measure current safely?

Correct polarity, never connect across a voltage source directly

What is the symbol for an ammeter?

Circle with an ‘A’

What is the unit for voltage?

Volt (V)

How is voltage measured in a circuit?

With a voltmeter in parallel across a component

How does a voltmeter connect in a circuit?

In parallel with the component to measure voltage across it

How do you convert volts to millivolts?

Multiply by 1000

What is the voltage across two 1.5V cells in series?

3V (add voltages)

How does voltage "drop" in a series circuit?

The sum of voltages across all components equals the supply voltage

How does voltage behave in a parallel circuit?

Each branch gets the full supply voltage

What does a voltmeter measure?

Electrical potential difference (voltage)

What is resistance?

Opposition to electric current

What is the unit for resistance?

Ohms (Ω)

How do you calculate resistance given voltage and current?

R = V ÷ I

How do you calculate I for a given V and R?

I = V ÷ R

How does resistance affect current?

Higher resistance = lower current (for given voltage)

How do you convert ohms to kilo-ohms?

1 kΩ = 1000 Ω; divide by 1000

How do you convert ohms to mega-ohms?

1 MΩ = 1,000,000 Ω; divide by 1,000,000

What does a fixed resistor do?

Limits or controls current to a set value in a circuit

What happens to current if resistance increases?

Current decreases

What happens to brightness if resistance in a lamp circuit increases?

Brightness decreases (less current)

In a parallel circuit, which branch gets more current?

The branch with lower resistance

What is a voltage divider?

Circuit with two resistors in series across a supply; divides voltage proportionally

What is the voltage divider formula for output voltage?

Vout = (R2 / (R1 + R2)) × Vin

If R1 = R2 in a voltage divider, what is Vout?

Half the supply voltage

What is the effect of resistor values in a divider?

Larger resistor gets a larger share of the voltage

How do you measure the voltage at a point on a circuit?

Use a voltmeter with one lead at the point, one at 0V rail

How do you plot IV characteristics?

Record V and I for various voltages, plot I vs V for component (resistor, lamp, diode)

What does a straight IV graph mean for a resistor?

Constant resistance (Ohmic conductor)

How does the IV graph of a filament lamp look?

Curved; resistance increases as current rises

Describe the IV characteristic for a silicon diode?

Almost no current for V < 0.7V, sharp increase for V > 0.7V (forward-biased)

What is electrical power?

Rate of energy transfer; measured in Watts (W)

What formula links power, voltage, current?

P = V × I

What formula links power, resistance, current?

P = I² × R

What formula links power, voltage, resistance?

P = V² ÷ R

How do you calculate energy from power and time?

E = P × t

If a lamp uses 60 mA at 6 V, what is its power?

P = 6 × 0.06 = 0.36 W (or 360 mW)

If a 48W lamp is connected to 12V, what is its current?

I = 48 ÷ 12 = 4 A

If a resistor has 20Ω and 0.2A flows, power?

P = 0.2² × 20 = 0.8 W

If a 100Ω resistor is across 9V, power?

P = 9² ÷ 100 = 0.81W

How do you use energy transfer formula?

Multiply power (W) × time (s) to get Joules (J)

If a lamp is 1.5W and on for 12s, how much energy?

E = 1.5 × 12 = 18J

Why use voltage divider circuits in electronics?

To provide reference voltages or scaled signals for sensors/inputs

If you want half the supply voltage from a divider, what values to use for R1 and R2?

R1 = R2 (equal values)

How is Ohm’s Law written?

V = I × R (voltage = current × resistance)