Year 9 Physics Revision - Vocabulary Flashcards

Static Electricity and Electrical Safety

• Static electricity is a build-up of charge (electrons) on objects.
• Electrical charge produces a force of attraction or repulsion between charged objects.
• The build-up of charge around an object can be described as a static electrical force field.
• Conductors and insulators affect how charge moves: conductors allow charge flow; insulators resist it.
• In homes, electrical safety relies on controlling current paths and providing protective devices.

Electric Circuits: Voltage, Current, Resistance, and Ohm's Law

• Voltage (V) is the energy given to charge as it moves around a circuit. It is the driving potential for current.
• A voltage drop across a circuit component represents energy transfer to that component (per charge).
• Current (I) is the flow of charge per second around a circuit.
• Current tends to flow from higher potential to lower potential.
• Resistance (R) is the restriction to the flow of charge through a circuit.
• Ohm's Law relates V, I, and R:
  V = I\,R
  I = \frac{V}{R}
  R = \frac{V}{I}
• Measuring tools:
  • Voltmeter measures voltage; typically connected in parallel across the component. Unit: volt (V).
  • Ammeter measures current; typically connected in series with the component. Unit: ampere (A).
  • Multimeter can measure both voltage and current (and sometimes resistance).
• Relationship between voltage, current, and resistance: for a fixed resistance, current is proportional to voltage; increasing voltage increases current; increasing resistance reduces current (for a given voltage).

Key concepts in circuits

• Movement of charge is electrical current.
• Symbols for common components (typical conventional representations):
  • Connecting wire
  • Light globe (lamp)
  • Battery
  • Switch
  • Voltmeter
  • Ammeter
  • Resistor
• Practical circuit tasks include drawing and constructing simple circuits using these components.

Representing Circuits and Home Safety

• Electrical hazards around the home include exposed wires, damaged cords, overloaded circuits, and faulty appliances.
• Fuses (or electrical breakers) protect circuits by interrupting current flow when it becomes too high.
• Modern Residual Current Devices (RCDs) detect leakage to earth and trip to prevent electric shocks.
• The earth (ground) circuit provides a safe path for fault currents, reducing shock risk.

Energy Transfer by Sound Waves and Wave Nature

• Sound is caused by vibrating particles; vibrations transfer energy from one medium to another.
• Sound travels as longitudinal waves consisting of compressions and rarefactions.
• A sound wave is characterized by:
  • Wavelength (λ)
  • Frequency (f)
  • Amplitude (A)
• The medium determines how sound propagates; sound requires a medium (air, water, solids) and cannot travel in a vacuum.

Representing and Interpreting Sound Waves

• Definitions:
  • Wavelength (λ): distance between consecutive crests (or troughs).
  • Frequency (f): number of cycles per unit time (Hz).
  • Amplitude (A): maximum displacement of particles from rest.
• Graphical interpretation: use wave graphs to determine λ, f, and A; changing amplitude, wavelength, or frequency alters the waveform accordingly.
• Relation to perception:
  • Amplitude relates to volume: larger A generally means louder sound.
  • Frequency relates to pitch: higher f means higher pitch.

Resonance and Its Applications

• Resonance is when an object vibrates at its natural (own) frequency.
• When an external force matches an object's natural frequency, energy transfer is maximized and the amplitude can grow significantly.
• Applications include musical instruments, engineering systems, and architectural design.
• Compare a musical note (coherent, periodic) with random noise (broad, irregular frequencies).

How Sound Travels Through Different Mediums

• Speed of sound varies by medium:
  • Typically fastest in solids, slower in liquids, slowest in gases.
• Reasons: density and elastic properties of the medium affect how quickly particles can transmit vibrations.
• Useful relation for travel time and distance: v = \frac{d}{t} where
  • v is speed of sound in the medium,
  • d is distance traveled,
  • t is time taken.

Glossary of Key Terms

• Static Electricity, Electric circuit, Voltage, Current, Resistance, Ohm’s law, RCDs, Fuse, Sound, Compressions, Rarefactions, Wavelength, Frequency, Amplitude, Pitch, Resonance.

Practice Questions and Worked Examples (Selected)

Section: Static Electricity and Measurement

1) How is static electricity created?

• When two insulators are rubbed together, surface charges are transferred from one object to the other, creating a static charge.

2) Charges of subatomic particles:

• Electron: - ext{ve}
• Proton: + ext{ve}
• Neutron: neutral (no charge)

3) Conductors vs insulators:

• Conductors: allow charge flow (low resistance).
• Insulators: inhibit charge flow (high resistance).

4) Classify items as Conductor (C) or Insulator (I):

• Pen: I
• Tennis ball: I
• Metal watch: C
• Wooden bat: I
• Water bottle: I
• Your pet dog: I
• Scissors: C
• House key: C

5) Measuring voltage vs current:

• Voltage: measured with a voltmeter in parallel across the component.
• Current: measured with an ammeter in series with the component.

6) Electric current and its unit:

• Definition: Flow of electrons; rate at which charge passes a point per second.
• Unit: ext{A} (ampere).

7) Relationship between current and voltage:

• In general, increasing voltage increases current for a given resistance (Ohm’s Law: I = V/R).
• If resistance changes, the relationship between V and I adjusts accordingly.

Section: Ohm’s Law and Calculations

8) Table: Definitions, Units, and Tools

• Current: Definition: Flow of electrons through a conductor; Unit: ext{A}; Tool: Ammeter.
• Voltage: Definition: Measure of energy given by the source; Unit: ext{V}; Tool: Voltmeter.
• Resistance: Definition: Difficulty for current to flow; Unit: \Omega; Tool: Multimeter (in practice).

9) Ohm’s Law explanation and practical use

• Core idea: The current in a circuit depends on the voltage supplied and the resistance opposing the current.
• Key equations:
  V = I R,
  I = \frac{V}{R},
  R = \frac{V}{I}
• Analogy: Current is like the speed of a car; voltage is like the push; resistance is like obstacles on the road.

10) Effect of changing voltage on current (constant resistance):

• If voltage increases, current increases: I \propto V (for constant R).
• If voltage decreases, current decreases: I \downarrow as V \downarrow (for constant R).

11) Effect of increasing resistance (constant voltage):

• As R increases, current I = V/R decreases.

12) Ohm’s Law in equation form:

• V = I R

13) Example 1: A resistor with V = 6\text{ V} and I = 0.5\text{ A}

• R = \frac{V}{I} = \frac{6}{0.5} = 12\ \Omega

14) Example 2: A train with V = 25\text{ V} and R = 45\ \Omega

• I = \frac{V}{R} = \frac{25}{45} \approx 0.56 \text{ A}

15) Circuit diagrams to draw (descriptive guide):

• i) A single cell, a light bulb, and a switch arranged so that the switch can open/close the circuit to switch the light on.
• ii) A cell, an ammeter, a globe (lamp), and a voltmeter arranged for measurement.
• iii) A battery, an open switch, an ammeter, a resistor, and three globes.

16) How to measure voltage correctly

• Tool: Voltmeter
• Connection: In parallel across the component or section of circuit where voltage is to be measured.

17) Wires and short circuits

• Damaged/frayed wires can cause short circuits where current bypasses intended paths.
• Consequences: overheating, fire risk, electric shocks, damage to devices.

18) Electrical safety devices

• Circuit Breaker: Intercepts abnormal current flow and interrupts the circuit to prevent damage or fire.
• Residual Current Device (RCD): Monitors imbalance between live and neutral; trips if leakage detected to prevent shock.
• Fuse: Melts when excessive current flows, breaking the circuit to prevent damage or fire.

Section: Sound, Waves, and Resonance Practice

1) Correct type of wave for sound travel:

• Longitudinal wave.

2) Definitions:

• Frequency: Number of complete cycles per unit time; measured in Hz.
• Wavelength: Distance between consecutive crests or troughs.
• Amplitude: Maximum displacement of particles from rest (related to loudness).

3) Why sound cannot travel in space:

• Space is a vacuum with no medium to transmit vibrations.

4) Amplitude and volume:

• Higher amplitude generally corresponds to louder volume; amplitude relates to energy of the wave.

5) Frequency and pitch:

• Higher frequency corresponds to higher pitch; lower frequency to lower pitch.

6) Regions created by particle movement:

• Compressions and rarefactions (in a longitudinal wave).

7) Labeling compressions and rarefactions (conceptual):

• Compressions: regions of high particle density (
• Rarefactions: regions of low particle density).

8) Sketching waves corresponding to compressions/rarefactions (conceptual guide):

• A wave with alternating dense (compression) and sparse (rarefaction) regions along the propagation direction.

9) Wave descriptions for given cases (textual description):

• High pitch, low amplitude: High frequency, small amplitude.
• Loud volume, low frequency: Large amplitude, low frequency.

Section: Speed of Sound and Applications

10) Lightning and thunder timing:

• Light travels faster than sound, so we see lightning before we hear thunder.

11) Sound speed in materials:

• Sound travels faster in solids (denser, stiffer media) than in gases; typically faster in a kitchen bench (solid) than in a sponge (porous, less dense).

12) Noise cancelling headphones (principle):

• Emit sound waves that are out of phase (opposite frequency) to cancel external noise through destructive interference.

13) Resonance (definition and occurrence):

• Resonance occurs when an external force matches an object's natural frequency, increasing the amplitude of oscillation.
• Everyday examples: tuning forks, musical instruments, engineering systems subject to periodic forces.

14) Speed of sound in air:

• Approximately v \approx 343\ \mathrm{m\,s^{-1}} at room temperature.

15) Sound in seawater:

• Given: v = 1500\ \mathrm{m\,s^{-1}}; time for sound to travel to the seabed and back: t = 0.4\ \mathrm{s}.
• One-way distance: d = v \cdot \frac{t}{2} = 1500 \cdot \frac{0.4}{2} = 600\ \mathrm{m}.

16) Temperature effect on sound speed in air:

• Sound travels faster in warm air than in cold air because molecular velocity is higher at higher temperatures.

17) Production of sound waves:

• Produced when an object vibrates, causing surrounding particles to vibrate and propagate waves.

18) Hearing a bell:

• A bell vibrating creates sound waves that travel through air; these waves cause the eardrum to vibrate, which is interpreted by the brain as sound.

19) Main components of a sound wave:

• Compression and Rarefaction.

20) Density and sound speed:

• Denser materials have more molecules to interact with, allowing faster propagation of sound (up to material limits).

21) Order of speed of sound in states of matter (from fastest to slowest):

• Solid (1) > Liquid (2) > Gas (3).

22) Speed of sound in air calculation:

• If lightning is 1100 m away and heard after 3 s, then
  v = \frac{d}{t} = \frac{1100\ \mathrm{m}}{3\ \mathrm{s}} \approx 366.67\ \mathrm{m\,s^{-1}}.

23) Echo distance (extension):

• If an echo is heard 5 s after shouting and the speed of sound in air is v = 342\ \mathrm{m\,s^{-1}}, then the distance to the canyon wall is:
  • Time for sound to reach the wall and return: 5 s
  • One-way travel time: \frac{5}{2} = 2.5\ \mathrm{s}
  • Distance: d = v \cdot t = 342 \cdot 2.5 = 855\ \mathrm{m}.