Practicals

• Independent variable

  The thing you change in an investigation
• Dependent variable


  The other thing that changes as a result of the independent variable, which you measure
• Control variables

  Variables that could change but are kept the same throughout to ensure accurate results
• Always state the piece of equipment used for each measurement
• Discuss the accuracy of measurements and how to reduce errors and uncertainties
• Multiple or repeat measurements should be taken to calculate a mean
• Specific heat capacity is the amount of energy needed to raise the temperature of 1 kg of a substance by 1°C
• Specific heat capacity practical

  Insert electrical heater into water or metal, measure mass, place thermometer, measure initial temperature, turn on heater, measure temperature every 20 seconds, measure current and PD using ammeter and voltmeter, rearrange equation to calculate specific heat capacity
• Resistance of a wire practical

  Use constantan wire, attach to battery with crocodile clips, measure current and PD, change distance between clips to change wire length, calculate resistance for each length, plot resistance against length to show a directly proportional relationship
• Rearranging Ohm's law


  Resistance is equal to voltage (PD) divided by current
• Plotting resistance against length

  Results in a directly proportional relationship that is a straight line going through the origin
• Varying PD across a fixed resistor

  Measured with a voltmeter in parallel with it, the current through it will change
• Changing a variable resistor in series with the fixed resistor


  Results in changing current
• Turning the battery round to get negative values of PD and current


  Produces a straight line going through the origin showing that the resistance is constant
• Components

  • Ohmic components have a constant resistance
  • Non-ohmic components have a resistance that varies
• Resistance in a filament bulb

  Results in a curve on the graph due to resistance increasing with higher current
• Temperature increase with higher current in a metal


  Causes ions to oscillate more, increasing the frequency at which electrons collide with them, making it harder for them to flow
• Diode behavior


  Only allows current to flow in one direction, high resistance in the other direction
• Finding density of objects or solutions

  1. For regular objects, measure dimensions and calculate volume to find density

  2. For irregular objects, use displacement method or Eureka can to find volume and calculate density
• Pure water has a density of 1 g per cm cubed
• Finding spring constant

  Hang slotted masses on a spring, measure extension, and plot force against extension to find spring constant
• Hooke's Law: F = kx, where k is the spring constant
• Verifying Newton's Second Law

  Attach slotted masses to a trolley, let them fall to accelerate the trolley, use light gates or stopwatch to calculate acceleration
• Using light gates to determine final velocity


  Use one light gate to get the final velocity and use Newton's equation of motion
• Using a stop clock to determine time taken


  Use a stop clock to get the time taken to go a certain distance and use another of Newton's equations to get the acceleration
• Changing the force accelerating the trolley

  Remove masses but place them on the trolley every time to keep the total mass constant, get the force by multiplying the mass by G
• Force against acceleration

  Should end up with a proportional relationship, a straight line going through the origin as F=ma
• Measuring waves using a ripple tank

  Use light to project an image of the waves onto a screen, measure the length of 10 waves and divide by 10 to get the wavelength
• Measuring waves using an oscillator


  Produce a stationary wave on a string with masses on the end over a pulley to provide tension, vary the frequency until you get the simplest stationary wave formed on the string
• Detecting infrared absorption

  Fill a lesli cube with hot water, use an infrared detector or infrared thermometer to detect heat radiated from each side
• Testing absorption of different materials


  Have boiling tubes wrapped in different materials with a thermometer through a bung in the top of each, shine a lamp on them and record their temperatures after a set time
• Testing insulation


  Wrap beakers of hot water in varying thicknesses or types of insulation with lids and thermometers, record the temperature drop over a certain time
• Finding the refractive index of a glass or perspex block

  Place the block on a piece of paper, shine light from a ray box in at an angle, draw around the block and mark where the ray enters and exits the block, measure the angle of incidence and angle of refraction