Core practicals: waves, light and electricity

Introduction to Core Practicals

In your GCSE Physics course, you don’t just learn theories; you also learn how to be a scientist! The core practicals are hands-on experiments that help you understand how waves, light, and electricity work in the real world. Even though there is no "practical exam," you will be asked about these experiments in your written papers.

Don't worry if you missed a lab or found it confusing—these notes will break down exactly what you need to know, from the equipment you use to the results you should expect.

Note: For help with units like the metre (m) or ampere (A), see the chapter "Key concepts of physics: SI units, prefixes and conversions".

Core Practical 4.17: Measuring Waves

This practical is all about finding the speed, frequency, and wavelength of waves. You need to know how to do this in two different environments: a fluid (water) and a solid (a metal rod).

1. Waves in a Fluid (Ripple Tank)

The Goal: To measure the speed of ripples on the water's surface.

The Method:
1. Set up a ripple tank with a motor-driven bar that creates straight waves.
2. Adjust the motor until you see clear waves on the paper below the tank.
3. To find wavelength (\(\lambda\)): Use a ruler to measure the distance across 10 wave fringes, then divide by 10. This is more accurate than measuring just one!
4. To find frequency (\(f\)): Count how many waves pass a fixed point in 10 seconds, then divide by 10.
5. To find speed (\(v\)): Use the formula \(v = f \times \lambda\).

2. Waves in a Solid (Metal Rod)

The Goal: To find the speed of sound waves traveling through a solid metal rod.

The Method:
1. Suspend a metal rod using elastic bands.
2. Tap one end of the rod with a hammer. This creates sound waves.
3. Use a microphone and a smartphone app (or oscilloscope) to record the peak frequency of the sound.
4. The wavelength (\(\lambda\)) in the rod is equal to twice the length of the rod (\(2 \times L\)).
5. Calculate speed using \(v = f \times \lambda\).

Key Takeaway: For both experiments, measuring over a larger distance or time (like 10 waves instead of 1) helps reduce experimental error.

Core Practical 5.9: Refraction in Glass Blocks

Refraction happens when light changes speed as it moves from one material (like air) into another (like glass), causing it to bend.

The Method:
1. Place a rectangular glass block on a piece of paper and trace around it.
2. Use a ray box to shine a thin beam of light into the block at an angle.
3. Mark the path of the incident ray (the light going in) and the emergent ray (the light coming out) with dots.
4. Remove the block and join the dots to show the path of the refracted ray inside the block.
5. Draw a normal (a line at \(90^{\circ}\) to the block's edge) where the light entered.
6. Measure the angle of incidence (\(i\)) and the angle of refraction (\(r\)) using a protractor.

What you will see: As light enters the glass, it slows down and bends towards the normal. As it leaves the glass back into the air, it speeds up and bends away from the normal.

Common Mistake: Make sure you measure your angles between the ray and the normal, NOT between the ray and the glass block!

Core Practical 5.19P: Thermal Radiation (Physics Only)

This practical investigates how different surfaces affect how much thermal (heat) energy is radiated or absorbed. This is only for students taking the Physics-only (separate science) route.

The Equipment: Usually a "Leslie Cube" (a metal box with four different sides: matt black, shiny silver, matt white, and shiny black).

The Method:
1. Fill the Leslie Cube with boiling water.
2. Use an infrared detector (or a thermometer with a blackened bulb) to measure the amount of radiation coming from each of the four surfaces.
3. Keep the distance between the cube and the detector the same for every side to make it a fair test.

The Results:
1. Matt Black: The best emitter and best absorber of radiation.
2. Shiny Silver: The worst emitter and worst absorber (it reflects radiation instead).

Quick Review: Think of a silver emergency blanket. It stays warm because the shiny surface is a poor emitter of heat, keeping the heat trapped inside!

Core Practical 10.17: Electrical Circuits

This practical has two parts. It helps you understand how current and potential difference (voltage) behave in different components and circuit types.

Part A: V-I Characteristics

The Goal: To see how the resistance changes for a fixed resistor and a filament lamp.

The Method:
1. Set up a series circuit with a power supply, an ammeter, and the component (resistor or lamp).
2. Place a voltmeter in parallel across the component.
3. Use a variable resistor to change the potential difference (\(V\)) and record the resulting current (\(I\)).
4. Repeat for several readings and then swap the battery connections to get negative values.

The Results:
- Fixed Resistor: The graph is a straight line through the origin. This means resistance is constant. \(V = I \times R\).
- Filament Lamp: The graph is an "S" shape. As the current increases, the lamp gets hot, and the resistance increases, which levels off the curve.

Part B: Series and Parallel Circuits

The Goal: To test how current and potential difference behave in different setups.

Key Rules to Remember:
- Series: The current is the same everywhere. The total potential difference is shared between components.
- Parallel: The total current splits at junctions. The potential difference across each branch is the same.

Did you know? If you add more resistors in parallel, the total resistance of the circuit actually decreases! It’s like opening more checkout lanes at a supermarket—the "flow" of shoppers (current) gets easier.

Summary Table: Core Practical Formulas

You may need to use these formulas when analyzing your practical data. Remember to check your "formulae sheet" in the exam!

Wave Speed: \(v = f \times \lambda\)
Wave Speed: \(v = x / t\)
Ohm's Law: \(V = I \times R\)
Electrical Power: \(P = I \times V\)

Exam Tips for Core Practicals

1. Identify Variables: Know your Independent Variable (what you change), Dependent Variable (what you measure), and Control Variables (what you keep the same to make it a fair test).
2. Safety First: Always mention safety! For example, "Be careful with boiling water in the Leslie Cube" or "Don't touch hot filament lamps."
3. Improve Accuracy: If a question asks how to make an experiment better, think about using digital sensors (like a light gate or infrared probe) to remove human reaction time, or taking multiple readings and calculating a mean.