AQA GCSE Physics Paper 2 Foundation Tier Exhaustive Study Guide

Space Physics and the Solar System

A group of stars is defined as a galaxy. The specific galaxy that contains our solar system is known as the Milky Way. Scientific evidence indicates that the Sun was originally formed from a large cloud of dust and gas. The primary force involved in the formation of the Sun from these materials was gravitational force.

Stars produce visible light and other forms of radiation because they release energy through a process called nuclear fusion, which occurs within their cores. When energy travels from the Sun to the Earth, it does so in the form of visible light and infrared radiation. Both types of radiation travel at the same constant speed, known as the speed of light, through the vacuum of space, meaning they take the same amount of time to reach the Earth.

In terms of wave properties, infrared radiation has a longer wavelength than visible light. Because frequency is inversely proportional to wavelength, the frequency of visible light is greater than the frequency of infrared radiation. Additionally, both the Sun and the Earth emit infrared radiation; however, the Sun emits it at a significantly greater rate. This is because the Sun has a much higher temperature than the Earth and possesses a much larger surface area.

Magnetism and Electromagnetism

Metals are categorized into magnetic and non-magnetic materials. Common magnetic metals include cobalt, iron, and nickel, while aluminium and copper are non-magnetic. Magnetic field lines represent the direction and strength of a magnetic field, always originating from the North (N) pole and directing toward the South (S) pole. The magnetic field is strongest at the poles of the magnet, where the field lines are most densely packed.

When two magnets are placed near each other, like poles repel. For instance, if two South (S) poles are facing each other, the magnetic field lines will curve away from the gap between them. A plotting compass can be used to demonstrate the magnetic effect of an electric current. When a current flows through a wire, it creates a magnetic field around it. Moving a compass around the wire changes the direction of the needle, and switching the current on or off causes the needle to move. If the current in the wire is decreased, the strength of the magnetic field around the wire decreases accordingly. Conversely, if the direction of the current is reversed, the direction of the magnetic field also reverses.

Forces, Acceleration, and Resultant Action

In an investigation regarding the acceleration of a trolley, several variables must be identified. The independent variable is the total mass of the trolley, which is deliberately changed by the student. The dependent variable is the acceleration of the trolley, which is measured. To ensure a fair test, the force pulling the trolley must be kept constant as a control variable. Friction is the force that prevents a trolley from moving when those driving forces are absent.

Mean acceleration can be calculated by summing multiple measured values and dividing by the total number of readings. For example, values of $1.58\,m/s^2$, $1.53\,m/s^2$, and $1.54\,m/s^2$ result in a mean acceleration of $1.55\,m/s^2$. The relationship between mass and acceleration is described as inversely proportional: as the total mass of the trolley increases, the acceleration decreases, provided the resultant force remains constant. This is governed by the equation $\text{resultant force} = \text{mass} \times \text{acceleration}$. For a trolley with a mass of $1.5\,kg$ and an acceleration of $0.62\,m/s^2$, the resultant force is calculated as $1.5 \times 0.62 = 0.93\,N$.

Wave Properties: Transverse and Longitudinal

A transverse wave is characterized by an amplitude and a wavelength. The amplitude is the maximum displacement from the equilibrium position, while the wavelength is the distance between two consecutive peaks or troughs. One example of a transverse wave that can travel through a vacuum is any form of electromagnetic radiation, such as light or radio waves. The period of a wave can be calculated using the formula $\text{period} = \frac{1}{\text{frequency}}$. For a frequency of $5000\,Hz$, the period is $0.0002\,s$.

Longitudinal waves, such as sound waves, consist of compressions and rarefactions. In a longitudinal wave, points at the centre of a rarefaction are areas where the particles are furthest apart. The wavelength of a sound wave can be determined using $\text{wavelength} = \frac{\text{wave speed}}{\text{frequency}}$. If the speed of sound in air is $330\,m/s$ and the frequency is $750\,Hz$, the wavelength is approximately $0.44\,m$. When a sound wave moves from air into water, its speed increases. Since the frequency remains constant, the wavelength must also increase.

Distance, Speed, and Motion Graphs

Quantities in physics are either scalar or vector. Scalar quantities, such as distance and speed, have only magnitude. Vector quantities, such as displacement, velocity, and force, have both magnitude and direction. On a distance-time graph, the total distance walked is the final value on the vertical axis. Average speed is calculated by dividing the total distance by the total time. For instance, a distance of $3200\,m$ covered in $2000\,s$ results in an average speed of $1.6\,m/s$.

The gradient of a distance-time graph represents the speed of the object. A flatter section (smaller gradient) indicates a slower speed. When a person walks up steps, they do physical work against the force of gravity. A typical speed for a person running is approximately $3.0\,m/s$, which is significantly faster than a typical walking speed.

Electromagnetic Radiation and Light

Electromagnetic radiation spans a wide range of wavelengths. Ultraviolet radiation has wavelengths between $100\,nm$ and $400\,nm$, visible light falls between $400\,nm$ and $700\,nm$, and infrared radiation is between $700\,nm$ and $1000\,nm$. Infrared can be detected using equipment such as an infrared camera, thermometer, or thermal imaging goggles. Red light typically has a wavelength near the upper end of the visible spectrum, such as $690\,nm$ or $750\,nm$.

Organisms perceive radiation differently. For example, bees can detect ultraviolet radiation that humans cannot, but they cannot see the full range of red light that humans can. When sunlight hits a red flower, the red light is reflected while all other colors are absorbed. If a red flower is viewed through a green filter, it will appear black because the filter absorbs the red light reflected by the flower. Reflection from rough surfaces, such as plant leaves, is known as diffuse reflection.

Pressure and Calculation of Weight and Velocity

Weight is the force exerted by gravity on an object and is calculated using $\text{weight} = \text{mass} \times \text{gravitational field strength}$. For a mass of $25000\,kg$ in a gravitational field of $9.8\,N/kg$, the weight is $245000\,N$. Pressure at the bottom of a container is calculated using $\text{pressure} = \frac{\text{force}}{\text{area}}$. For a force (weight) of $1960000\,N$ over an area of $49\,m^2$, the pressure is $40000\,Pa$. Pressure in fluids acts in all directions, exerting force perpendicular to surfaces.

Acceleration is the rate of change of velocity, calculated as $\text{acceleration} = \frac{\text{change in velocity}}{\text{time taken}}$. A child accelerating from $0.70\,m/s$ to $1.3\,m/s$ over $5.0\,s$ has an acceleration of $0.12\,m/s^2$. In vertical motion, the final velocity of an object falling from rest can be found using $v^2 - u^2 = 2as$. For a fall of $0.95\,m$ with acceleration due to gravity of $9.8\,m/s^2$, the final velocity is approximately $4.3\,m/s$.

Elasticity and Springs

Hooke's Law states the relationship between force and extension: $\text{force} = \text{spring constant} \times \text{extension}$, represented as $F = k \times e$. The spring constant ($k$) measures the stiffness of the spring. If a force of $336\,N$ causes a change in length of $0.21\,m$, the spring constant is $1600\,N/m$. Percentage change in length is determined by dividing the change by the original length and multiplying by 100. For example, a decrease of $0.21\,m$ on an original length of $0.84\,m$ is a $25\%$ change.

Refraction and Light Practical

Refraction is the bending of light as it passes from one medium to another. A common practical involves using a glass block, a ray box, and a protractor. The student draws around the block, marks the path of the incident and emergent rays, and joins them to show the path through the block. The angle of incidence ($i$) and angle of refraction ($r$) are measured relative to a normal line at $90^{\circ}$ to the surface.

The resolution of a standard protractor is typically $1^{\circ}$. Data from refraction experiments showed that the angle of refraction is not directly proportional to the angle of incidence because the graph of $r$ versus $i$ is a curve rather than a straight line through the origin. In reflection, the angle of incidence equals the angle of reflection. This principle applies to headlights, where lamps and reflective surfaces direct light forward.

Work, Moments, and Gears

Work done is the energy transferred when a force moves an object and is calculated by $\text{work done} = \text{force} \times \text{distance}$ ($W = F \times s$). If a child does $35\,J$ of work to push a walker $2.8\,m$, the applied force is $12.5\,N$. When a child moves from a carpet to a hard floor, the resistive force (friction) decreases; if the child applies the same horizontal force, the resultant force increases, causing the walker to accelerate.

A moment is the turning effect of a force, calculated as $\text{moment} = \text{force} \times \text{perpendicular distance}$ ($M = F \times d$). For a force of $2.0\,N$ applied $7.5\,cm$ ($0.075\,m$) from a pivot, the moment is $0.15\,Nm$. In a system of gears, Gear A exerts a force on Gear B. Because they are interlocked, Gear B will rotate in the opposite direction to Gear A.

Predicted Topics: Thermal and Static Electricity

Thermal conductivity measures how quickly energy is transferred through a material. Materials with low thermal conductivity, such as wool, bubble wrap, or thick foam, are better insulators. In houses, roof insulation using materials like fibreglass reduces the rate of energy transfer, saving homeowners money on heating. A lower thermal conductivity means energy is lost more slowly.

Static electricity occurs through the transfer of electrons. When a plastic rod is rubbed with a dry cloth, electrons move from the cloth to the rod, giving the rod a negative charge. If two objects have the same charge, they will repel each other, while opposite charges attract. An uncharged object can be attracted to a charged one through induction. Contact with a grounded frame, such as a trampoline frame, causes the charge to flow through the body, resulting in a static shock as the body discharges.

Radioactivity and the National Grid

Atoms consist of a dense central core called the nucleus, which contains protons and neutrons, surrounded by electrons. Protons are positive, neutrons are neutral, and electrons are negative. Radioactive decay involves the emission of radiation: Alpha (stopped by paper), Beta (stopped by aluminium), and Gamma (stopped by lead). Half-life is the time required for the initial count rate of a radioactive isotope to decrease by half. Irradiation refers to exposure to radiation rays, while contamination occurs when radioactive material actually sticks to an object.

The National Grid uses transformers to transfer electricity efficiently. Step-up transformers increase potential difference and decrease current to reduce energy loss as heat in cables over long distances. Step-down transformers then decrease the potential difference to safer levels for use in homes. Renewable energy sources like wind turbines are carbon-neutral but can be less reliable than coal due to weather variance.

Questions & Discussion

Question 01.7: How does the rate of infrared radiation emitted by the Sun compare with the rate emitted by the Earth, and why? Answer: The Sun emits infrared at a greater rate than the Earth because it is at a much higher temperature (and has a larger surface area).

Question 02.5: Describe how a plotting compass can be used to demonstrate the magnetic effect of a current. Answer: The teacher can move the plotting compass around the wire. Switching the current on and off causes the needle to move, showing the magnetic field's presence.

Question 05.4: Which section of the distance-time graph (A, B, or C) shows the person walking the slowest? Answer: Section B, because the incline (gradient) of the graph is least steep compared to the other sections.

Question 09.1: What is the resultant vertical force on a child standing still in a baby walker? Answer: The resultant vertical force is $0\,N$ because the child is not accelerating vertically; the upward and downward forces are balanced.

Question 09.4: Explain why the speed of the baby walker increased despite applying the same force when moving from carpet to a hard floor. Answer: The resistive force (friction) decreased, which caused the total resultant force to increase.