Required practicals 14-21: physics

Introduction to Physics Required Practicals

Welcome! In your AQA GCSE Combined Science: Trilogy course, there are 8 specific Physics practicals (numbered 14 to 21) that you must know inside out. You won't be graded on how you perform them in class, but you will be asked about them in your exams. These questions make up about 15% of your total marks!

Don't worry if you find the equipment or the equations a bit intimidating at first. We are going to break each one down into a clear method, the variables you need to control, and the "why" behind the science. Let's get started!

Required Practical 14: Specific Heat Capacity

The goal of this practical is to find out how much energy is needed to raise the temperature of 1kg of a material by \(1^\circ\text{C}\).

The Method

1. Measure the mass of a block of material (like aluminium) using a balance.
2. Place an immersion heater and a thermometer into the holes in the block.
3. Connect the heater to a power supply and a joulemeter (this measures energy).
4. Wrap the block in insulation (like bubble wrap) to stop heat escaping.
5. Record the starting temperature.
6. Turn on the power and wait for the temperature to rise by about \(10-20^\circ\text{C}\).
7. Record the final temperature and the total energy shown on the joulemeter.

Key Formula

You will use: \( \Delta E = m c \Delta \theta \)
To find the specific heat capacity (\( c \)), we rearrange it to: \( c = \frac{\Delta E}{m \Delta \theta} \)

Quick Tip: If your value for specific heat capacity is higher than expected, it's usually because some thermal energy escaped into the air. This is why insulation is so important!

Required Practical 15: Resistance

This practical has two parts: looking at how the length of a wire affects resistance, and comparing resistors in series and parallel.

Part 1: Length of a Wire

1. Set up a simple circuit with a battery, an ammeter, and a voltmeter across a test wire.
2. Use crocodile clips to attach the wire to the circuit at different lengths (e.g., 10cm, 20cm, 30cm).
3. For each length, record the current (\( I \)) and potential difference (\( V \)).
4. Calculate resistance using \( R = \frac{V}{I} \).

The Result: As the length of the wire increases, the resistance increases. It is a directly proportional relationship (a straight line through the origin on a graph).

Part 2: Series and Parallel

Compare the total resistance of two identical resistors when they are in one long loop (series) versus when they are on separate branches (parallel).
- Series: Total resistance increases.
- Parallel: Total resistance decreases.

Required Practical 16: I-V Characteristics

Here, we investigate how the current (\( I \)) through a component changes as we change the potential difference (\( V \)) across it.

The Setup

You need a circuit with a power supply, a variable resistor (to change the voltage), an ammeter, and the component you are testing.

The Components to Know:

1. Fixed Resistor: Gives a straight line graph through the origin. Current is directly proportional to potential difference.
2. Filament Lamp: Gives an "S" shaped curve. As it gets hotter, the resistance increases, so the graph levels off.
3. Diode: Current only flows in one direction. The graph stays at zero for negative voltages and then shoots up suddenly in the positive direction.

Common Mistake: Forgetting to swap the battery leads to get negative readings! To get the full graph, you must measure the component in both directions.

Required Practical 17: Density

Density is simply how much "stuff" (mass) is packed into a certain space (volume).

Regular Objects (like a cube)

1. Measure the mass using a balance.
2. Measure the length, width, and height with a ruler. Multiply them to get the volume.
3. Calculate: \( \text{density} = \frac{\text{mass}}{\text{volume}} \) or \( \rho = \frac{m}{V} \).

Irregular Objects (like a stone)

1. Measure the mass.
2. Fill a Eureka can (displacement can) with water until it's level with the spout.
3. Lower the object into the water. The volume of water that drips out into a measuring cylinder is the exact volume of the object.
4. Calculate density using the same formula.

Required Practical 18: Force and Extension

This investigates Hooke’s Law using a spring.

The Method

1. Hang a spring from a clamp stand and measure its natural length with a ruler.
2. Add a weight (force) to the bottom.
3. Measure the new length and subtract the original length to find the extension.
4. Repeat by adding more weights.

Key Rule: The extension of the spring is directly proportional to the force applied, provided you don't exceed the limit of proportionality (the point where the spring is permanently stretched).

Formula: \( F = k e \) (Force = spring constant \(\times\) extension).

Required Practical 19: Acceleration

This looks at Newton's Second Law: \( F = m a \).

The Method

1. Use a toy car or trolley on a track, pulled by a string with weights hanging over a pulley.
2. Use light gates or a stopwatch to measure the acceleration.
3. To test Force: Keep the mass of the whole system the same, but move weights from the trolley to the hanging hook.
4. To test Mass: Keep the force (hanging weights) the same, but add mass to the trolley.

Important Note: If you add mass to the trolley, the acceleration will decrease. If you increase the pulling force, the acceleration will increase.

Required Practical 20: Waves

You need to measure the speed of waves in two different environments.

1. In a Liquid (Ripple Tank)

- Use a vibrating bar to create waves in a shallow tank of water.
- Use a ruler to measure the distance across 10 wave crests, then divide by 10 to find the wavelength (\( \lambda \)).
- Count how many waves pass a point in 10 seconds and divide by 10 to find the frequency (\( f \)).
- Calculate speed: \( v = f \lambda \).

2. In a Solid (Vibrating String)

- Use a signal generator to make a string vibrate.
- Adjust the frequency until you see a clear "loop" (standing wave).
- Measure the wavelength and use the same formula \( v = f \lambda \).

Required Practical 21: Infrared Radiation

This investigates how different surfaces emit or absorb thermal radiation.

Using a Leslie Cube

A Leslie cube has four different surfaces: Matt black, Shiny black, White, and Shiny silver.
1. Fill the cube with boiling water.
2. Point an infrared detector at each surface from the same distance.
3. Record the amount of infrared radiation emitted.

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

Did you know? This is why emergency "space blankets" are shiny silver—to stop your body heat from being radiated away!

Summary Key Takeaways

1. Units matter: Always check if you need to convert grams to kilograms or cm to meters.
2. Variables: In every practical, identify the Independent variable (what you change), the Dependent variable (what you measure), and the Control variables (what you keep the same to make it a fair test).
3. Accuracy: Using digital equipment (like light gates or digital thermometers) often reduces human error, making your results more accurate.