Electricity & Magnetism
A premium, fully interactive guide to Section 4 of the Cambridge O Level Physics (5054) syllabus. Explore dynamic simulations and comprehensive notes.
4.1 Simple Magnetism
Understand the foundational forces between magnetic poles, methods of magnetisation/demagnetisation, and how to map magnetic field patterns.
4.2 Electrical Quantities
Dive into core metrics: charge ($Q$), current ($I$), voltage ($V$), and resistance ($R$). Explore I-V characteristic graphs for non-ohmic components.
4.4 Practical Electricity
Calculate electrical power and energy usage ($kWh$). Study critical domestic safety mechanisms including trip switches, fuses, earthing, and double insulation.
4.5 Electromagnetic Effects & 4.6 Scope
Master the Right-Hand Grip Rule, D.C. motors, Faraday's Law, A.C. generators, transformers in high-voltage grids, and oscilloscope interpretation.
4.1 Simple Magnetism
Magnetic Poles: Magnets feature a North (N) and South (S) pole. The fundamental law states: Unlike poles attract, like poles repel.
Magnetic Field: A defined region in which a magnetic pole experiences a force. The field lines always travel from the North pole to the South pole.
Methods of Magnetisation & Demagnetisation
Magnetisation
- 1. Stroking: Stroke a magnetic material (like steel) with one pole of a permanent magnet repeatedly in the same direction. This aligns the magnetic domains.
- 2. D.C. Solenoid (Electrical): Place the material inside a solenoid (coil of wire) and pass a large Direct Current (D.C.) through it. The strong, steady magnetic field aligns the domains permanently.
Demagnetisation
- 1. Heating: Heat the magnet until it is red hot. The increased thermal energy randomises the domains.
- 2. Hammering: Hammer the magnet vigorously while it lies in an East-West direction (to avoid the Earth's magnetic field re-aligning it).
- 3. A.C. Solenoid (Best Method): Place the magnet in a solenoid carrying an Alternating Current (A.C.), then slowly withdraw it in an East-West direction. The rapidly changing A.C. field scrambles the domains.
π‘ Pro Tip: When using the A.C. solenoid method for demagnetisation, withdrawing the magnet slowly is crucial. It ensures the magnet experiences a gradually decreasing alternating magnetic field, leaving domains completely randomised.
Magnetic Materials
- βΉ Magnetic: Iron, steel, cobalt, nickel.
- βΉ Non-magnetic: Copper, plastic, wood.
- βΉ Temporary (Soft Iron): Magnetises/demagnetises easily. Used in electromagnets.
- βΉ Permanent (Steel): Hard to magnetise but retains magnetism.
Interactive: Magnetic Field Explorer
Move your mouse/finger over the canvas to act as a compass. Notice how the red needle (North) aligns with the field lines pointing towards the South pole.
Definitions & In-Depth Explanation
- Induced Magnetism: When an unmagnetised magnetic material is placed in a magnetic field, it temporarily becomes a magnet. The pole induced nearest the magnet is always the opposite of the inducing pole.
- Magnetic Shielding: Soft iron can be used to protect sensitive equipment from magnetic fields. The field lines prefer to travel through the permeable iron rather than the air.
- Domain Theory (In-Depth): Magnetic materials consist of tiny atomic magnets called "domains". In an unmagnetised state, domains point in random directions, cancelling each other out. When magnetised, these domains align in the same direction.
Practice Examples
Solution: They will repel each other, as like poles repel.
Solution: A North pole is induced. Induced magnetism always creates an opposite pole nearest to the inducing magnet, resulting in attraction.
Solution: When the power is switched off abruptly, the A.C. current stops at a specific, random value. The magnet will be left weakly magnetised in whichever direction the field was pointing at that exact fraction of a second. To properly demagnetise, the magnet must be slowly withdrawn while the A.C. is still flowing.
4.2 Electrical Quantities
Electrical Charge ($Q$): Measured in Coulombs ($C$). Like charges repel, unlike charges attract. An electric field is a region where a charge experiences a force.
Interactive: Electric Field Simulator
Drag the positive (Red) and negative (Blue) test charges to see how the electric field vectors (arrows) change in real-time based on Coulomb's Law.
Current, Voltage, Resistance & Meters
Current ($I$) & Ammeters
The rate of flow of charge. Measured in Amperes ($A$).
Must be connected in series so the full current flows through it. It has very low resistance to avoid affecting the circuit.
Potential Difference ($V$) & Voltmeters
Work done per unit charge. Measured in Volts ($V$).
Must be connected in parallel across the component to measure the drop in potential. It has very high resistance so it draws minimal current.
Resistance ($R$): Opposes current flow, measured in Ohms ($\Omega$). ($R = V/I$). Depends on length (proportional) and cross-sectional area (inversely proportional).
Non-Ohmic Characteristics (I-V Graphs)
While an Ohmic Resistor obeys Ohm's law (constant resistance), many real-world components like filament lamps and diodes are non-ohmic. Their resistance changes as the current or voltage changes.
Interactive: Component I-V Graph Explorer
Current (I) vs Voltage (V)
Alternating Current (AC) vs Direct Current (DC)
Interactive: AC & DC Visualizer
Observe how DC flows continuously in one direction, while AC oscillates. Adjust the sliders to see the gradual change on the electron flow (diagram) and voltage over time (graph).
Voltage vs Time
Definitions & In-Depth Explanation
- Filament Lamp (Non-Ohmic): As voltage increases, the current increases, which causes the filament to heat up. This increase in temperature causes the atoms in the metal lattice to vibrate more, increasing resistance. Hence, the graph curves, showing a decreasing gradient.
- Electromotive Force (e.m.f): The electrical work done by a source in moving a unit charge around a complete circuit. ($E = W/Q$). While similar to p.d., e.m.f refers strictly to the energy *supplied* to the circuit.
- Factors affecting Resistance: A wire's resistance is given by $R = \rho L / A$. Increasing length ($L$) increases resistance. Increasing cross-sectional area ($A$) (thicker wire) decreases resistance.
Practice Examples
Solution: The voltmeter must be connected in parallel across the lightbulb.
Solution: A decreasing gradient on an I-V graph means the resistance is increasing ($R = V/I$). As voltage increases, the current heats the filament, increasing the collision rate of electrons with the metal lattice, which increases the resistance.
Solution: Since $R \propto L/A$, doubling the length multiplies $R$ by 2. Halving the area multiplies $R$ by 2 again. Total multiplier is $2 \times 2 = 4$. New resistance = $40 \ \Omega$.
4.2 Charge, Conduction & Circuit Sources
Electrostatic Charging by Friction
What happens: When two different insulating materials are rubbed together, electrons are transferred from one surface to the other. Because both materials started neutral (equal + and β charge), the one that gains electrons becomes negatively charged, and the one that loses electrons becomes positively charged, with an equal amount of charge.
Diagram: Rubbing a Polythene Rod
Key Rule to Remember
Only electrons move during charging by friction β never protons (they are locked inside the nucleus) and never "positive charge" as a physical thing. A material becomes positive purely because it has lost some of its electrons.
| Pair rubbed together | Becomes (β) | Becomes (+) |
|---|---|---|
| Polythene rod + wool duster | Polythene | Wool |
| Acetate/perspex rod + silk cloth | Silk | Acetate |
| Balloon + hair/wool jumper | Balloon | Hair/jumper |
Everyday examples & applications: Rubbing a balloon on your hair makes it stick to a wall (induced attraction); a comb pulled through dry hair picks up small bits of paper; clothes "crackle" and cling together after tumble-drying because different fabrics rub together and charge up; a Van de Graaff generator uses a moving rubber belt rubbing against rollers to build up a huge charge; photocopiers and laser printers use charged drums by friction/light to attract toner powder onto paper.
π‘ Exam tip: Always describe charging in terms of electron transfer, not "charge is created". State clearly which object loses electrons (β positive) and which gains electrons (β negative), and that the magnitude of charge gained equals the magnitude lost β charge is conserved.
Electrical Conductors vs Insulators
Conductors
Materials that contain free (delocalised) electrons which can move easily through the material, allowing charge/current to flow.
Examples: copper, aluminium, iron, silver, graphite (carbon), and other metals; also salt solutions and the human body (contain free ions).
Insulators
Materials whose electrons are tightly bound to their atoms/molecules, so there are no (or very few) free charge carriers available to move.
Examples: plastic (PVC), rubber, glass, dry wood, air, ceramic, pure water.
Interactive: Test the Material (Conductor or Insulator?)
This is the standard school experiment: a cell, a lamp, and two crocodile-clip leads are connected in series with a gap. A test material is placed in the gap. If the lamp lights, current is flowing, so the material is a conductor. If the lamp stays off, the material is an insulator.
Procedure: (1) Set up cell, lamp and leads in series with a gap. (2) Connect the crocodile clips to either end of the test sample. (3) Observe the lamp. (4) Repeat with several materials and record results in a table of "Conductor" / "Insulator".
The Electron Model of Conduction
In a metal: Each metal atom releases one or more outer-shell electrons into a shared "sea" of free (delocalised) electrons that can move throughout the whole lattice of fixed positive metal ions. This is why metals conduct electricity (and heat) so well.
Interactive: Electron Drift vs Conventional Current
Toggle the switch to connect the cell. Watch the blue electrons physically drift (slowly!) from β to +, while the yellow conventional current arrow is drawn flowing the opposite way, from + to β, around the external circuit.
Conventional Current
Defined historically (before electrons were discovered) as flowing from the positive terminal, around the circuit, to the negative terminal. All circuit diagrams, current arrows and formulas ($I = Q/t$) use this direction.
Electron Flow (Real Carriers)
The actual free electrons move from the negative terminal to the positive terminal β the exact opposite direction to conventional current, since electrons carry negative charge.
π‘ Why the mix-up exists: Benjamin Franklin defined the direction of "positive" current flow in the 1700s, long before J.J. Thomson discovered the electron in 1897. By the time scientists realised the actual charge carriers in metals are negative electrons moving the other way, the "conventional current" convention was already used worldwide β so physics kept both: conventional current for circuit analysis, and electron flow for describing what is truly happening inside the wire.
Ammeters: Analogue and Digital, and Choosing a Range
Analogue Ammeter
Has a needle that deflects across a printed scale. Often has two or more ranges (e.g. 0β1 A and 0β5 A) selected via different terminals β you must read the scale that matches the terminal in use, and start on the largest range if the current is unknown.
Digital Ammeter
Displays the current directly as a number, avoiding parallax/reading errors. Ranges are usually selected automatically ("auto-ranging") or with a rotary dial, and precision is limited by the number of digits shown.
Choosing/using a range β tips: (1) Always start on the highest range if you don't know the expected current, then switch down for better precision if the reading is small. (2) Never connect an ammeter of too small a range where a large current is expected β it can overload and damage the meter. (3) An ammeter must always be placed in series and has very low resistance so it barely affects the circuit's current.
Combining Sources: e.m.f. in Series and in Parallel
Interactive: Cell Arrangement Explorer
Each cell here has an e.m.f. of 1.5 V. Choose an arrangement and adjust the number of cells to see the total e.m.f. calculated live.
Series sources: The e.m.f.s add up: $E_{total} = E_1 + E_2 + ... + E_n$ (cells connected + to β, to +, to β ...). This is how a torch with 2 or 3 cells gets a higher voltage to light the bulb brighter.
Parallel, identical sources: The combined e.m.f. is equal to that of just one cell β it does not add up. What you gain instead is a greater capacity to supply current for longer (a longer-lasting battery), since each cell only has to supply part of the total current.
Experiment: Determining Resistance with an Ammeter and Voltmeter
Circuit Diagram
Procedure
- Connect the resistor (or test wire) in series with a cell, an ammeter, and a variable resistor/rheostat (to change the current).
- Connect a voltmeter in parallel across just the resistor being tested.
- Close the switch and record the ammeter reading ($I$) and voltmeter reading ($V$).
- Adjust the rheostat to get several different pairs of $I$ and $V$ readings.
- Plot a graph of $V$ (y-axis) against $I$ (x-axis). Draw a best-fit straight line through the origin.
- Calculate resistance from the gradient of the graph: $R = \text{gradient} = V/I$.
Interactive: Build the VβI Graph
Drag the slider to set a voltmeter reading, then click "Take Reading" to plot a point (a fixed test resistor of 5 Ξ© is used, with small realistic scatter). Watch the best-fit gradient update β that gradient is the resistance!
π‘ Precision tips: Take several readings and repeat each one to check for consistency. Keep the resistor's temperature roughly constant (don't leave a high current flowing for a long time, as heating changes resistance). A best-fit line through the origin that curves suggests a non-ohmic component (like a filament lamp), not a constant resistance.
Practice Examples
Solution: Electrons transferred from the wool to the polythene rod, so the wool lost electrons and became positively charged, with charge equal in size to the rod's negative charge.
Solution: In series: $E = 4 \times 1.5 = 6.0\text{ V}$. In parallel (identical cells): total e.m.f. stays at just $1.5\text{ V}$ (same as one cell) β the parallel arrangement only increases how long the current can be supplied, not the e.m.f.
Solution: $R = V/I = 4.0/0.8 = 5\ \Omega$. The line might not pass exactly through the origin due to a zero error in the ammeter or voltmeter (needs correcting before readings), or contact resistance at the crocodile clips adding a small constant offset.
4.4 Practical Electricity
Electrical Power ($P$): The rate at which electrical energy is transferred by an electric circuit. Measured in Watts ($W$).
Interactive: Fuse Safety Simulator
A fuse breaks the circuit if the current exceeds its rating (e.g., 13A). Increase the power of the appliance to see how a high current melts the fuse wire, protecting the circuit.
Mains Voltage: 240V
Definitions & In-Depth Explanation
- The Kilowatt-hour (kWh): A commercial unit of electrical energy. It is the energy consumed by a 1 kW (1000 W) appliance operating for 1 hour. Total Cost = Energy (kWh) Γ Price per kWh.
- Live, Neutral, and Earth (In-Depth): The Live wire (Brown) delivers current at high voltage. The Neutral wire (Blue) completes the circuit at ~0V. The Earth wire (Green/Yellow) is a safety wire connected to the metal casing of an appliance to prevent electrocution.
- Fuses & Circuit Breakers: A fuse contains a thin wire that melts if the current gets too high, breaking the circuit. It must always be placed on the Live wire. Circuit breakers (MCBs) perform the same job but can be reset magnetically/thermally without replacing parts.
Practice Examples
Solution: $P = V \times I = 240 \times 10 = 2400 \text{ W (or 2.4 kW)}$.
Solution: $I = P/V = 1000/240 \approx 4.17 \text{ A}$. You must choose a fuse slightly higher than the operating current, so the 5A fuse is correct.
Solution: Daily Energy = $2.5 \text{ kW} \times 8 \text{ h} = 20 \text{ kWh}$.
Monthly Energy = $20 \times 30 = 600 \text{ kWh}$.
Total Cost = $600 \times 0.15 = \$90.00$.
4.4 Uses of Electricity & Electrical Safety
Common Uses of Electricity
Heating
kettles, heaters, toasters
Lighting
lamps, LEDs, streetlights
Battery Charging
phones, laptops, EVs
Powering Motors
fans, washing machines
Electronic Systems
phones, computers, TVs
Why Lamps Are Connected in Parallel in a Lighting Circuit
Switch between circuit types, then click "Blow Lamp 2" to see the difference. In a domestic lighting circuit, lamps (and sockets) are always wired in parallel.
Advantage 1 β Independence: If one lamp fails (filament breaks) or is switched off, the circuit at that point breaks β but the other lamps stay lit because they are on separate parallel branches, not the same loop.
Advantage 2 β Full, equal voltage: Every lamp gets the full supply voltage (e.g. 230 V mains) across it, so each shines at its normal, rated brightness β unlike in series, where the voltage is shared out and lamps would be dim.
Hazards When Using a Mains Supply
β‘ Damaged Insulation
If the plastic/rubber coating around a live wire is cut, cracked, or worn through, the bare live conductor can be touched directly, or it can touch a metal case β both risk electric shock or starting a fire.
π‘οΈ Overheating Cables
If a cable carries more current than it is rated for, resistive heating ($P = I^2R$) can make it dangerously hot, melting the insulation and risking a fire. Coiled-up cables and cables covered by rugs/furniture trap heat and make this worse.
π§ Damp Conditions
Water conducts electricity (especially with dissolved salts/ions), and damp skin has much lower resistance than dry skin. Using electrical appliances with wet hands, or in a damp bathroom, greatly increases the current that could pass through the body β far more dangerous.
π Overloading Sockets/Extension Leads
Plugging too many high-power appliances into one socket, extension lead or multi-plug adaptor draws a total current beyond what the wiring was designed for β again causing overheating and fire risk, even if each individual appliance seems fine.
Trip Switches (Circuit Breakers)
Operation: A trip switch (MCB/circuit breaker) monitors the current flowing through it. If the current exceeds a set safe value, an internal electromagnet (or bimetallic strip) is triggered, which mechanically flips the switch to instantly break the circuit β much faster than a fuse wire melting.
Fuse
- Thin wire that melts (one-time use) when current is too high.
- Cheap, but must be physically replaced after it blows.
- Reacts slightly slower β takes a moment to heat up and melt.
Trip Switch (Circuit Breaker)
- Uses an electromagnet/bimetallic strip to flip mechanically.
- Can simply be reset (switched back on) β no replacement needed.
- Reacts almost instantly, giving better protection.
Choosing the Correct Fuse Rating or Trip-Switch Setting
Standard fuse ratings you should know: 1 A, 3 A, 5 A, 13 A. The rule: choose the smallest standard rating that is still greater than the appliance's normal operating current β this protects the appliance as tightly as possible while never blowing under normal use.
π‘ Worked logic: A microwave rated 1000 W on 240 V draws $I = P/V = 1000/240 β 4.17$ A. The 3 A fuse is too small (would blow immediately under normal use); the next size up, 5 A, is just above the operating current β correct choice. The same logic sets a trip switch's current rating.
What Happens When a Live Wire Touches an Earthed Metal Case
Click the button to simulate a fault: the live wire's insulation fails inside the appliance and it touches the earthed metal casing.
The physics: Because the earth wire has an extremely low resistance path straight to the ground, when the live wire touches the case, a very large current suddenly flows from live β case β earth wire β ground. This huge surge instantly blows the fuse (or trips the circuit breaker) in the live wire, disconnecting the supply before anyone touching the case could receive a dangerous shock. Without the earth wire, the case itself would become live at mains voltage β touching it could be fatal.
Why the Casing Must Be Earthed or Double-Insulated
Earthed Metal Casing
Appliances with a metal (conducting) outer case are connected to the earth wire. If the live wire ever touches the casing accidentally, the earth wire instantly provides a safe, low-resistance path for the fault current, blowing the fuse and cutting power β the case never stays "live" long enough to shock someone.
Double Insulation
Appliances with a plastic (insulating) outer case β like hairdryers or drills β don't need an earth wire at all, because the casing itself is an insulator. It is physically impossible for the live wire to make the outer surface live, since there's an extra layer of insulation between the live parts and anything you can touch. Marked with the symbol β‘ (a square inside a square).
Why the Switch, Fuse and Circuit Breaker Must Be in the Live Wire
If the switch, fuse, or circuit breaker were placed in the neutral wire instead of the live wire, opening it would stop the current flowing β but the live wire and the whole appliance would remain connected to the dangerous live mains voltage all the way up to the appliance, even while it appears "off". Anyone opening the appliance to repair it (thinking it's safe because it's switched off) could then receive a fatal shock. Placing the switch/fuse/breaker in the live wire ensures that once it opens, the appliance side is completely disconnected from the high-voltage supply.
Switch in live wire: Switching off fully isolates the appliance from mains voltage β safe to touch internal live parts (though you should still unplug/isolate before repairing).
Fuse/breaker in live wire: When it blows/trips, it cuts the live supply at the earliest point, before the fault current can reach the rest of the appliance or its casing.
Practice Examples
Solution: Any two of: damaged insulation exposing live conductors; overheating cables (e.g. from overloading); using appliances in damp conditions; overloading sockets/extension leads.
Solution: In parallel, each lamp receives the full supply voltage so all shine at normal brightness, and each lamp can be switched on/off or can fail independently without affecting the others β unlike in series, where one failed lamp would break the whole circuit and turn all lamps off.
Solution: The earth wire provides a path of very low resistance to the ground. By $I = V/R$, this low resistance causes a very large current to flow suddenly through the live wire, earth wire, and fuse. This large current exceeds the fuse's rating, melting it (or tripping the circuit breaker) almost instantly, which disconnects the live supply before a person touching the casing could be exposed to a dangerous voltage for any significant time.
4.5 Electromagnetic Effects
Magnetic Effect of a Current
A current-carrying wire produces a magnetic field. The shape of the field depends on the shape of the wire (straight vs. solenoid).
Straight Wire & Grip Rule
The field consists of concentric circles. Use the Right-Hand Grip Rule: Point your right thumb in the direction of conventional current ($+$ to $-$), and your fingers curl in the direction of the magnetic field lines.
3D Interactive Solenoid
The magnetic field pattern around a solenoid is identical to that of a bar magnet. Drag to rotate the 3D model.
The Motor Effect & D.C. Motors
When a current-carrying wire is placed in a magnetic field, it experiences a force (The Motor Effect). Fleming's Left-Hand Rule helps determine the direction of this force.
Align the fingers of your left hand at right angles to each other:
- ThuMst: Motion / Thrust (Force)
- First: Magnetic Field (North to South)
- SeCond: Current (Positive to Negative)
In a D.C. motor, the split-ring commutator reverses the direction of the current in the coil every half-turn. This ensures the force on each side of the coil reverses simultaneously, allowing the motor to rotate continuously in the same direction.
Interactive: Electromagnetic Induction
Drag the magnet quickly in and out of the coil. The faster you move it (rate of change), the larger the induced voltage on the galvanometer. Observe the graph plot the EMF.
Induced EMF vs Time
2D Reference Diagram: Faraday's & Lenz's Law
The A.C. Generator
A coil rotating in a magnetic field cuts the field lines, inducing an alternating e.m.f. Carbon brushes and slip rings maintain an electrical connection without tangling the wires.
Interactive: A.C. Generator Simulation
Watch the coil rotate between the magnetic poles. Adjust the speed and field strength to see the gradual change in the generated sine wave e.m.f.
Generated EMF vs Time
3D Interactive Diagram: A.C. Generator Components
Drag to rotate β’ Scroll to zoom
Transformers & High-Voltage Transmission
Transformers operate on AC only. A changing current in the primary coil induces a changing magnetic field in the iron core, which induces an e.m.f. in the secondary coil.
Interactive: Transformer Diagram
Change the number of turns below. The visual diagram dynamically updates the number of coils wrapped around the iron core based on your inputs.
Step-Down Transformer
Why Transmit at High Voltage?
Step-up transformers increase transmission voltage, which drastically reduces the current ($I = P/V$). A lower current significantly reduces heat loss in the transmission cables ($P_{loss} = I^2 R$).
Definitions & In-Depth Explanation
- Faraday's Law & Lenz's Law (In-Depth): Faraday discovered that a changing magnetic environment (flux) induces an EMF. The size of this EMF is directly proportional to the rate of change of flux. Lenz's Law is a consequence of the conservation of energy: the induced current will create a magnetic field that actively resists the motion that created it (e.g., pushing a North pole into a coil induces a North pole to repel it).
- A.C. Generator Function: As the coil rotates, it continuously cuts the magnetic field lines. The angle of cutting changes, which is why the output is an alternating sine wave. At 90Β° (horizontal), it cuts the lines fastest, giving peak voltage. At 0Β° (vertical), it slides parallel to the lines, giving zero voltage.
- Transformer Core Laminations: The iron core is laminated (made of thin slices separated by insulation) to reduce eddy currents. These are unwanted currents induced in the core itself that would cause massive energy loss in the form of heat.
Practice Examples
Solution: Stepping up the voltage decreases the current flowing through the grid cables. Lower current reduces power lost as heat due to the resistance of the cables ($P = I^2R$).
Solution: It reverses the direction of the current in the coil every half revolution. This ensures that the force on each side of the coil always acts in the same direction, keeping the motor spinning continuously.
Solution: The voltmeter will read 0V. A transformer only works with Alternating Current (AC). DC produces a constant magnetic field. Since the magnetic field is not changing, there is no change in magnetic flux, and therefore no EMF is induced in the secondary coil according to Faraday's Law.
4.6 Oscilloscope
Y-Gain (Voltage): Determines the vertical scale (Volts per division). Used to measure peak potential difference (amplitude).
Timebase: Determines the horizontal scale (Time per division). Used to measure the period of the wave to calculate frequency ($f = 1/T$).
Interactive: Cathode Ray Oscilloscope
Definitions & In-Depth Explanation
- Cathode Ray Oscilloscope (CRO): An instrument used to display, measure, and analyze waveforms of electrical signals. It operates by firing an electron beam (cathode ray) at a fluorescent screen.
- X and Y Plates (In-Depth): The Y-plates deflect the electron beam vertically based on the input voltage (controlled by the Y-Gain). The X-plates deflect the beam horizontally at a steady rate, sweeping from left to right to represent time (controlled by the Timebase circuit).
- Measuring DC vs AC: A DC signal will appear as a single flat horizontal line shifted above or below the center zero line. An AC signal will appear as a continuous sine wave oscillating across the center zero line.
Practice Examples
Solution: Peak Voltage = Divisions $\times$ Y-Gain = $3 \times 2 = 6 \text{ V}$.
Solution: Period ($T$) = $4 \text{ div} \times 5 \text{ ms/div} = 20 \text{ ms} = 0.02 \text{ seconds}$.
Frequency ($f$) = $1 / T = 1 / 0.02 = 50 \text{ Hz}$.
Solution: With the timebase off, the beam does not sweep left to right. It will only deflect vertically. $12\text{V} / 5\text{V/div} = 2.4$ divisions. The student will see a single stationary glowing dot, 2.4 divisions above the center crosshair.