Practicals Flashcards
Describe a method for investigating the relationship between force and extension for a spring
- Measure natural length of string with mm ruler clamped to stand
- Take reading at eye level & add marker to bottom of spring to make reading more accurate
- Add mass to spring & allow spring to come to rest
- Record mass and measure new length of spring (extension is change in length)
- Repeat process until you have enough measurements (no fewer than 6)
When doing a light experiment, where should you do it?
In a dim room
Why should you do a light experiment in a dim room?
- So you can clearly see paths of (thin) rays of light
- Allows you to trace them more accurately = more exact angle measurements
Describe how you could use transparent materials to investigate refraction
Use a drawing to help you
By seeing how much light = refracted when it passes from air into different materials
- Place transparent rectangular block (e.g. glass) on piece of paper & trace around it
- Use ray box/laser to shine ray of light at middle of one side of the block
- Trace incident ray & mark where light ray emerges on other side of block
- Remove block and, with straight line, join up incident ray and emerging point = to show path of refracted ray through block
- Draw normal at point where light ray entered block
- Use protractor to measure angle of incidence & angle of refraction
- Repeat experiment using rectangular blocks (e.g. Perspex) made from different materials, keeping incident angle same throughout
When using transparent materials to investigate refraction, what would be the result and why?
Result: Angle of refraction changes for different materials
∵ their different optical densities
Describe how could investigate how light reflected depending on the smoothness of the surface
Use a drawing to help you
- Take piece of paper & draw straight line across it
- Place an object so one of its sides line up with this line
- Shine ray of light at object’s surface and trace the incoming & reflected light beams
- Draw normal at point where ray hits object
- Use protector to measure angle of incidence & angle of reflection & record these values in a table
- Make note of width + brightness of reflected light ray
- Repeat experiment for range of objects
What is the result when investigating how light is reflected depending on the smoothness of the surface?
- Smooth surfaces (e.g. mirrors) give clear reflections
- Reflected ray is as thin and bright as incident ray
- Rough surfaces (e.g. paper) cause diffuse reflection
- Reflected beam is wider and dimmer (or not observable at all)
What does the term ‘I-V characteristics’ refer to?
Refers to graph = shows current (I) flowing through a component changes as pd (V) across it is increased
What kind of I-V characteristic do non-linear components (e.g. filament lamp or diode) have?
Have cured I-V characteristic
What kind of I-V characteristic do liner components (e.g. an
ohmic conductor) have?
Have an I-V characteristic that’s a straight line
Describe how you can investigate the I-V characteristics of a
filament lamp, a diode and a resistor (at constant temperature)
Use a drawing to help you
- Set up test circuit shown below
- Begin to vary variable resistor
- = alters current flowing through circuit & pd across component
- Take several pairs of readings from ammeter and voltmeter = shows how pd across the component varies as current changes
- Repeat each reading twice more = get an average pd at each current
- Swap over wires connected to cell = direction of current is reversed
- Plot a graph of current against voltage for component
Draw the graph (result) for a diode
Explain the graph (result) for a diode
- Current will only flow through diode in one direction
- Diode has very high resistance in reverse direction
Draw the graph (result) for a filament lamp
Explain the graph (result) for a filament lamp
- As current increases = temperatures of filament increases = resistance increases
- Means less current can flow per unit pd
- = Graph gets shallower - hence the curve
Draw the graph (result) for a ohmic conductor
Explain the graph (result) for a ohmic conductor
- Current through an ohmic conductor (at a constant temperature) = is directly proportional to potential difference
- ∴ Get a straight line
Name 2 risk assessment for investigating the cooling curve of stearic acid
- Safety goggles must be worn throughout
- DO NOT attempt to pull thermometer out of solidified stearic acid (when you have finished)
Describe how you would investigate the strength of an electromagnets (number of turns on coil)
- Wind 50 turns of wire into coils around iron nail
- Add iron nail to circuit with variable power supply, ammeter and switch
- Place nail in clamp stand
- Close switch in circuit
- Switch on power supply & gradually increase voltage until there’s enough current flowing to support one paper clip
- Record value of current
- Now wind 100 turns of wire on to nail
- Adjust power supply so that current is same as before
- Record how many paper clips electromagnet can support
- Repeat this for 150 and 200 turns, BUT take care that coil of wire does not get too hot (If it does, switch off immediately)
- Plot graph
Describe how you would investigate the strength of an electromagnets (value of current)
- Wind 50 turns of wire into coils around iron nail
- Add iron nail to circuit with variable power supply, ammeter and switch
- Place nail in clamp stand
- Close switch in circuit
- Switch on power supply & gradually increase voltage until there’s enough current flowing to support one paper clip
- Record value of current
- Increase current until it will support 2 paper clips
- Record current
- Repeat this for up to 6 paper clips, BUT take care that coil of wire does not get too hot (if it does, switch off immediately)
- Plot a graph
