PHYSICS PAPER 1 NOTES

Energy Stores and Systems

Definition of a System: A system is defined as an object or a group of objects. When a system changes, there are changes in the way energy is stored.
Energy Transfer Situations: * An object thrown upwards: The person performs 'work' on the ball. Energy transfers from the chemical energy store of the person’s arm to the kinetic energy store of the ball. The chemical store decreases as the kinetic store increases. * A car accelerated by a constant force: Energy transfers from the chemical store of a battery or fuel (petrol) to the kinetic store of the car. The chemical store decreases while the kinetic store increases. * A moving object hitting an obstacle (e.g., a car hitting a wall): The force between the car and the wall performs 'work'. Kinetic energy from the car is transferred to the thermal store and elastic store of both the car and the wall. Some energy is also transferred away via sound waves. * A vehicle slowing down: Friction between brakes and wheels performs 'work'. Energy transfers from the car’s kinetic store to the thermal store of the brakes. The kinetic store decreases and the thermal store of the brakes increases. * Bringing water to a boil in an electric kettle: Energy is transferred into the kettle via an electrical pathway, causing the thermal energy store of the water to increase.
The Bouncing Ball Analysis: 1. At the highest point, Gravitational Potential Energy ( $E_p$ ) is at its maximum; the ball is stationary, so Kinetic Energy ( $E_k$ ) is $0\,J$ . 2. As the ball drops, $E_p$ is transferred to the $E_k$ store. 3. Just before impact, $E_p$ is $0\,J$ and $E_k$ is at its maximum speed. Upon hitting the floor, $E_k$ is transferred to the Elastic Potential Energy ( $E_e$ ) store as the ball squashes. 4. The ball rebounds, transferring energy back to the $E_k$ store. 5. As the ball gains height, $E_k$ transfers to $E_p$ . At the peak of the bounce, the ball is temporarily stationary ( $E_k = 0\,J$ ) and $E_p$ is at its maximum. 6. Energy Dissipation: In every bounce, energy is dissipated due to friction with the air, which is why the ball eventually stops.

Changes in Energy Calculations

Exam Step Procedure for Calculations: * Step 1: Select the correct equation from the formula sheet. * Step 2: Convert any units to standard units. * Step 3: Substitute the known quantities into the equation. * Step 4: Evaluate the numeric answer. * Step 5: Round the answer to the correct number of significant figures. * Step 6: Add the required units.
Kinetic Energy ( $E_k$ ): * Formula: $E_k = \frac{1}{2}mv^2$ * $E_k$ is kinetic energy in joules ( $J$ ). * $m$ is mass in kilograms ( $kg$ ). * $v$ is speed in metres per second ( $m/s$ ).
Gravitational Potential Energy ( $E_p$ ): * Formula: $E_p = mgh$ * $E_p$ is gravitational potential energy in joules ( $J$ ). * $m$ is mass in kilograms ( $kg$ ). * $g$ is gravitational field strength ( $N/kg$ ). On Earth, $g = 9.8\,N/kg$ . * $h$ is height in metres ( $m$ ).
Elastic Potential Energy ( $E_e$ ): * Formula: $E_e = \frac{1}{2}ke^2$ * Note: This only applies if the spring hasn't exceeded its elastic limit. * $E_e$ is elastic potential energy in joules ( $J$ ). * $k$ is the spring constant in newtons per metre ( $N/m$ ). * $e$ is extension in metres ( $m$ ).
Thermal Energy Change ( $\Delta E$ ): * Formula: $\Delta E = mc\Delta \theta$ * $\Delta E$ is change in thermal energy in joules ( $J$ ). * $m$ is mass in kilograms ( $kg$ ). * $c$ is specific heat capacity in $J/kg\,^{\circ}C$ . * $\Delta \theta$ is temperature change in degrees Celsius ( $^{\circ}C$ ).
Power ( $P$ ): * Definition: Power is the rate at which energy is transferred or the rate at which work is done. * Units: An energy transfer of $1\,joule\,per\,second$ is equal to a power of $1\,watt\, (W)$ . * Formula 1: $P = \frac{E}{t}$ ( $E$ = energy transferred in $J$ , $t$ = time in $s$ ). * Formula 2: $P = \frac{W}{t}$ ( $W$ = work done in $J$ , $t$ = time in $s$ ).
Work Done Linkage: Work done is synonymous with energy transferred. In 6-mark questions, students often must link two equations (using one to find a quantity, then substituting it into a second).

Specific Heat Capacity Required Practical

Definition: The amount of energy required to raise the temperature of $1\,kg$ of a substance by $1\,^{\circ}C$ .
Aim: To determine the specific heat capacity (SHC) by linking the decrease of one energy store to the increase in temperature of a metal block.
Method: 1. Measure the mass of the metal block using a balance. 2. Insert the heater into the block and record the initial temperature with a thermometer. 3. Turn on the power and start a stopwatch. 4. Record potential difference ( $V$ ) and current ( $I$ ) to calculate power ( $P = IV$ ). 5. After $10\,minutes$ ( $600\,seconds$ ), turn off the power and record the final temperature. 6. Calculate $\Delta \theta = \text{final temperature} - \text{initial temperature}$ . 7. Calculate total energy supplied: $E = Pt$ . 8. Rearrange formula to $c = \frac{\Delta E}{m\Delta \theta}$ and solve.
Experimental Errors: * Systematic Error: Meters must be zeroed to avoid zero error. * Energy Dissipation: Heat escaping to surroundings or heating the thermometer makes the measured SHC higher than the actual value. Solution: Fully insulate the block. * Reading Errors: Read the thermometer at eye level to avoid parallax error or use a digital temperature probe and data logger. * Equipment Improvement: A joulemeter can measure energy directly, eliminating errors from voltage, current, and time measurements.
Graph Method: Plot Energy Transferred ( $J$ ) on the X-axis and Temperature ( $^{\circ}C$ ) on the Y-axis. The SHC can be determined from the gradient using: $c = \frac{1}{\text{gradient} \times m}$ .

Conservation and Efficiency of Energy

Principle of Conservation of Energy: Energy can be transferred usefully, stored, or dissipated, but it cannot be created or destroyed.
Closed Systems: In a closed system (e.g., a room where energy doesn't escape), the total energy remains constant even as it transfers stores.
Energy Dissipation: All transfers involve some energy being wasted (dissipated) as heat to surroundings.
Reducing Unwanted Transfers: * Lubrication: Using oil in machines reduces friction and dissipation. * Thermal Insulation: Materials with low thermal conductivity reduce the rate of energy transfer by conduction. Thick walls also lower the rate of cooling.
Efficiency: * Formula 1: $\text{Efficiency} = \frac{\text{useful output energy transfer}}{\text{total input energy transfer}}$ * Formula 2: $\text{Efficiency} = \frac{\text{useful power output}}{\text{total power input}}$ * Note: Efficiency is always between $0$ and $1$ (or $0\%$ and $100\%$ ). Use decimal values (e.g., $0.63$ for $63\%$ ) in calculations.

National and Global Energy Resources

Renewable Energy: Can be replenished as used (will not run out). Examples: Biofuel, Wind, Hydroelectricity, Geothermal, Tidal, Solar, Water Waves.
Non-renewable Energy: Cannot be replenished (will run out). Examples: Fossil Fuels (coal, oil, gas) and Nuclear fuel.
Reliability: Non-renewables are more reliable as they provide energy regardless of weather. Renewables like wind and solar depend on environmental conditions.
Energy Resource Comparison Table: * Fossil Fuels: Reliable, meets demand, can ramp up quickly. Disadvantages: Releases $CO_2$ (global warming), $SO_2$ (acid rain), mining damage, oil spills. * Nuclear: Reliable, no greenhouse gases, high energy density ( $per\,gram$ ). Disadvantages: Dangerous radioactive waste, risk of contamination if accidents occur. * Wind: No pollution, no permanent landscape damage. Disadvantages: Unreliable (no wind = no power), vulnerable to storm damage. * Solar: Reliable in sunny climates, no pollution. Disadvantages: High construction energy/cost, no power at night, cannot ramp up for demand spikes. * Geothermal: Very reliable (rocks always hot), no greenhouse gases. Disadvantages: Limited to specific geological locations. * Hydroelectric: Very reliable in rainy areas, no polluting gases, immediate response to demand. Disadvantages: Flooding valleys destroys habitats and releases $CO_2$ from rotting plants. * Wave/Tidal: No polluting gases. Disadvantages: Disturbs sea beds/habitats, kills fish, waves depend on wind (tidal is more predictable). * Biofuel: Carbon neutral (takes in same $CO_2$ as it releases), reliable. Disadvantages: Large scale forest clearing reduces biodiversity.
Global Trends: Energy use increased in the $1900s$ due to population and appliance growth. Currently reducing due to efficiency and environmental awareness. Switching to renewables is hindered by high costs, existing infrastructure, and perceived unreliability.

Electricity: Charge, Current, and Resistance

Definitions: * Current ( $I$ ): Rate of flow of electrical charge (delocalised electrons). Measured in Amps ( $A$ ). * Charge ( $Q$ ): Measured in Coulombs ( $C$ ). Formula: $Q = It$ . * Potential Difference ( $V$ ): Measure of energy transferred per unit charge. Measured in Volts ( $V$ ). * Resistance ( $R$ ): Opposition to current flow. Measured in Ohms ( $\Omega$ ).
Ohm’s Law: $V = IR$ .
Required Practical: Resistance of a Wire: * Independent Variable: Length of wire. * Dependent Variable: Resistance. * Method: Use crocodile clips to measure current and PD across different lengths of wire ( $10\,cm$ to $1\,m$ ). Calculate $R = \frac{V}{I}$ . * Result: Resistance is directly proportional to length (straight line through origin). * Accuracy: Use low current and switch off between readings to prevent heat-related resistance changes. Set clips exactly at zero (avoid zero error).

Resistors and Circuit Components

LDR (Light Dependent Resistor): In bright light, resistance decreases; in dark, resistance increases. Used in security lights (parallel connection to LDR increases PD across light as it gets dark).
Thermistor: In heat, resistance decreases; in cold, resistance increases. Used in thermostats to turn on fans.
I-V Characteristics Practical: * Fixed Resistor: Ohmic conductor. $I$ is directly proportional to $V$ (constant temperature). Straight line graph. * Filament Lamp: Non-ohmic. As current increases, temperature increases, ions vibrate faster, and more frequent electron collisions increase resistance. Curve graph. * Diode: Non-ohmic. Current flows in one direction only. Very high resistance in the reverse direction. Graph only shows current for positive PD.
Calculations for Non-Ohmic Components: Draw a tangent at the desired voltage; $\text{Resistance} = \frac{1}{\text{gradient of tangent}}$ .
Series vs. Parallel Rules: * Series: $I$ is same everywhere; $V_{total}$ is shared; $R_{total} = R_1 + R_2 ...$ * Parallel: $I$ is split between branches; $V$ is same in every loop; $R_{total}$ is less than the smallest individual resistor.

Mains Electricity and the National Grid

Supplies: * Direct Current (DC): Travels in one direction (cells/batteries). * Alternating Current (AC): Constantly changes direction. UK mains is $230\,V$ at $50\,Hz$ .
Three Core Cable: * Live (Brown): Carries $230\,V$ AC. * Neutral (Blue): Completes circuit at $0\,V$ . * Earth (Green/Yellow): Safety wire ( $0\,V$ ). Provides low resistance path to ground if a fault makes metal casing live, melting the fuse.
Power Formulas: * $P = VI$ * $P = I^2 R$
Energy Formulas: * $E = Pt$ * $E = QV$
The National Grid: System of cables and transformers. * Step-up Transformers: Increase PD, decrease current. Benefits: Lower current reduces heat dissipation in wires, making transmission efficient. * Step-down Transformers: Decrease PD to safe levels ( $230\,V$ ) for homes. * Transformer Equation Calculation: For an ideal transformer, input power equals output power: $V_p I_p = V_s I_s$ . * Example: Primary $240\,V$ , Secondary $12\,V$ , Primary current $20\,A$ . * $240 \times 20 = 12 \times I_s \rightarrow 4800 = 12 I_s \rightarrow I_s = 400\,A$ .

Particle Model and Atomic Structure

Density ( $\rho$ ): $\rho = \frac{m}{V}$ . * Practical: Use a balance for mass. Use a ruler/vernier callipers for regular volume ( $l \times w \times h$ ). For irregular objects, use a Eureka (displacement) can; volume of displaced water equals object volume.
Internal Energy: Total kinetic energy (motion) and potential energy (bonds) of all particles in a system.
States of Matter: Transitions (melting, freezing, etc.) are physical changes. Mass is conserved, but density changes.
Latent Heat ( $L$ ): Energy required for a change of state with no change in temperature. Formula: $E = mL$ . * Fusion: Solid/Liquid transition at melting point.