6.1 Identifying Appropriate Apparatus

• When planning an experiment, the first step is to identify the apparatus required
  • Each experiment will have its own unique set of apparatus
• The apparatus is the equipment needed to carry out the experiment
  • This includes both what you are measuring and how you are measuring it
• Common apparatus include:
  • Metre rulers - to measure distance and length
  • Balances - to measure mass
  • Protractors - to measure angles
  • Stopwatches - to measure time
  • Ammeters - to measure current
  • Voltmeters - to measure potential difference
• More complicated instruments such as the micrometer screw gauge and Vernier calipers can be used to more accurately measure length

Examples of apparatus used in scientific experiments

• The apparatus required depends on what you are trying to measure
• A few examples are shown in the table below

Apparatus Table

• An example of apparatus for measuring the specific heat capacity of an aluminium block is shown below:

Apparatus needed to measure specific heat capacity

• This includes:
  • A block of the substance (preferably 1kg in mass) or in the case of a fluid, a beaker containing a known mass of the fluid
  • A thermometer
  • An appropriate heater (e.g. an immersion heater)
  • A power source
  • A joule meter or a voltmeter, ammeter and stop-clock (I will assume we have the latter)
  • Wires and connectors

Range & Resolution of Instruments

• All instruments have a range and resolution
  • The range is the highest and lowest value an instrument can measure
  • The resolution is the smallest increment an instrument can measure

• Examples of resolutions for instruments are:

• These are just examples of ranges and resolutions for these devices
  • For example, some multimeters may have a bigger or smaller range depending on their model
• The resolution of an instrument gives its absolute uncertainty for a digital device
  • For an analogue device, such as a thermometer, ruler or top-pan balance, the uncertainty is ± half the resolution

Step 1: State the necessary measurements to be taken

• • The diameter of the wire
  • The initial length of the wire
  • The extension of the wire (final length – initial length)
  • The mass of the hanging masses or the weight applied to the wire

Step 2: State and explain which equipment would be the most suitable

For measuring the diameter of the wire:

• • A micrometer screw gauge or vernier callipers
  • Micrometer would be best as this has the highest resolution when measuring small areas

For measuring the original length / extension of the wire:

• • A metre ruler or a tape measure
  • The wire has a moderate length which cannot be measured using a vernier scale

For measuring extension:

• • Travelling microscope
  • These are designed for measuring small changes in length

For measuring the mass:

• • Scales or a top-pan balance
  • A top-pan balance would be best as this has the higher resolution
  • W = mg equation can be used to calculate weight

For measuring the weight directly:

• • A newton-meter
  • This is useful if ‘known’ weights are used and to check if the quoted masses are accurate

Step 3: Explain how Young's modulus can be determined from these measurements

• • Young modulus is equal to the gradient of a stress-strain graph (in the linear region)
  • Stress is equal to:

• • Strain is equal to:

Where:

• • F = weight (N)
  • A = cross-sectional area of wire (m²)
  • ΔL = extension (m)
  • L = original length (m)

• Young's modulus for this metal is then calculated using the following equation:

• The resolution is given by the smallest increment that the thermometer can read
  • For thermometer 1 this is 0.01 °C
  • For thermometer 2 this is 0.1 °C
• Therefore, thermometer 1 has the better resolution