Physics praticals paper 1 Flashcards
(17 cards)
Investigating a Resistor (Ohmic Conductor)
Set up a circuit with a resistor, ammeter, voltmeter, variable resistor, and battery.
(The ammeter goes in series; the voltmeter goes in parallel with the resistor.)
Use the variable resistor to adjust the current in the circuit.
(This changes the potential difference across the resistor.)
Record the current (from the ammeter) and the potential difference (from the voltmeter).
(These are your I and V values — put them in a results table.)
Repeat step 3 several times, adjusting the variable resistor each time.
(This gives you a range of readings.)
Reverse the battery connections to swap the direction of current and potential difference.
Take new readings for current and voltage again with the battery reversed.
(This shows how current behaves in both directions — it should just be negative values.)
Plot a graph of current (I) on the y-axis vs potential difference (V) on the x-axis.
(For a resistor, this gives a straight line through the origin.)
Conclude that the resistor is an ohmic conductor, because current is directly proportional to voltage.
(This only works if temperature is kept constant.)
Investigating a Filament Lamp
Same steps as before
- Replace the resistor with a filament lamp in the same circuit.
Adjust the variable resistor and record current and voltage, as before.
(The lamp gets hotter as current increases.)
Repeat for a range of values, then reverse the battery and take more readings.
Plot a graph of I vs V for the filament lamp.
(The graph will be a curve — not a straight line.)
Conclude that resistance increases as the lamp gets hotter.
(This shows it’s non-ohmic, because current is not proportional to voltage.)
Investigating a Diode
Replace the lamp with a diode, and add a fixed resistor in series.
(This protects the diode from high current.)
Use a milliammeter instead of a normal ammeter.
(Because current in a diode is very small at first.)
Adjust the variable resistor and record current and voltage for several values.
(You’ll see little or no current at first.)
Reverse the battery and take more readings.
Plot the I–V graph for the diode.
(It looks like a “hockey stick” — current flows in one direction only.)
Conclude that the diode only allows current to flow when the voltage is around 0.6–0.7 V in the forward direction, and blocks current in the reverse direction.
(This shows the diode has very high resistance in reverse.)
Specific heat capacity pratical
Place the beaker on a balance and press zero.
(This removes the mass of the empty beaker.)
Add the oil to the beaker and record the mass of the oil.
(You need the mass to calculate specific heat capacity.)
Place a thermometer and an immersion heater into the oil.
(These will measure temperature change and provide energy to the oil.)
Record the starting temperature of the oil.
Wrap the beaker in insulating foam.
(This reduces energy loss to the surroundings.)
Connect a joule meter to the immersion heater.
(This measures the total energy transferred to the oil.)
Leave the heater switched on for about 30 minutes.
(Allows enough time for a measurable temperature change.)
Record the number of joules of energy supplied from the joule meter.
Record the final temperature of the oil.
Sources of Inaccuracy in the Specific Heat Capacity Practical (and How to Reduce Them):
Thermal energy passing out of the beaker into the air - Solution: Use an insulator with a low thermal conductivity around the beaker (e.g. foam with a reflective surface).
Not all thermal energy goes into the oil (some heats the container or surroundings) - Make sure the immersion heater is fully submerged in the oil and in good thermal contact.
Inaccurate reading of the thermometer - Use an electronic temperature probe (reduces human error and increases precision).
Uneven distribution of thermal energy in the oil - Stir the oil gently before taking the final temperature (ensures uniform heating).
Thermal Insulators Practical Method (Water)
Place a small beaker inside a larger beaker.
(This creates a space for the insulating material.)
Boil water using a kettle.
Carefully transfer 80 cm³ of hot water into the small beaker.
(Use a measuring cylinder for accuracy.)
Place a lid (e.g. cardboard) on top of the large beaker.
(The lid must have a hole for the thermometer.)
Insert a thermometer through the hole in the lid.
Ensure the bulb of the thermometer is fully submerged in the hot water.
Start the stopwatch and record the initial temperature of the water.
Record the temperature every 3 minutes for a total of 15 minutes.
Repeat the experiment using the same volume of hot water, but with a different insulating material (e.g. bubble wrap, cotton wool, polystyrene) placed in the gap between the two beakers.
Eqipment for Investigating the Effect of Wire Length on Resistance
Battery or power supply
Ammeter
Voltmeter
Meter ruler
Length of constantan or nichrome wire
Two crocodile clips
Variable resistor (for extension)
Connecting wires
Switch
Investigating the Effect of Wire Length on Resistance
Attach a length of wire to a meter ruler using tape.
(Make sure it’s straight and tightly secured.)
Connect the wire into a circuit using two crocodile clips.
(Only the section between the clips is part of the circuit.)
Connect an ammeter in series and a voltmeter in parallel across the wire.
(The ammeter measures current, the voltmeter measures potential difference.)
Use a low potential difference from the power supply to avoid heating the wire.
Record the current and potential difference. use in V = I x R
Move one of the crocodile clips to change the length of wire in the circuit (e.g. test 10 cm, 20 cm, 30 cm, etc.).
Repeat steps 5–6 for several lengths and record all readings in a table.
Calculate resistance for each length using V =I x R
Plot a graph of resistance (y-axis) against length (x-axis).
(You should see a straight line — resistance is directly proportional to length.)
+ The graph should be a straight line through the origin if temperature is controlled.
This shows that resistance is directly proportional to wire length.
SOURCES OF ERROR & HOW TO REDUCE THEM (Investigating the Effect of Wire Length on Resistance)
Zero Error
- What (The voltmeter or ammeter may show a reading even when it should be zero.)
- Cause (Poor contact with crocodile clips or equipment not reset.)
- Fix: Subtract the zero error from all results. This is a systematic error and can’t be removed by repeats.
Heating effect of the wire
- What: Wire heats up as current flows, increasing resistance.
Fix:
Use low voltage to reduce current.
Only switch on the current while taking readings.
Using a Variable Resistor in a Circuit – Step-by-Step Explanation
Set up a circuit with a power supply, ammeter, component (e.g. lamp or wire), and variable resistor in series.
(The variable resistor controls the resistance of the whole circuit.)
Use connecting wires to include the variable resistor properly.
(Make sure the slider or dial on the resistor is accessible.)
Switch on the circuit briefly to take measurements.
(This prevents heating and keeps readings accurate.)
Move the slider on the variable resistor to change the resistance.
(Sliding changes the length of wire the current flows through, which changes total resistance.)
Record the current (ammeter) and potential difference (voltmeter if needed) for different positions of the slider.
(This allows investigation of how current and/or brightness changes as resistance increases.)
Repeat for several different resistance settings and plot results as required.
(Example: current vs voltage graph for a lamp.)
How to Determine the Density of Regular Solid Iron Objects
Place the object on a balance and record its mass (in grams or kilograms).
(This gives you the mass, m.)
Use a ruler to measure the length of each side of the object (in cm or m).
(For a cube, you can just measure one side.)
Calculate the volume using the formula: Volume = length^3
Calculate density using formula D = M/V
For Irregular Solid Objects (e.g. Roughly Shaped Iron Object)
Place the object on a balance and record its mass.
Fill a Eureka can (displacement can) with water up to just below the spout.
Place an empty measuring cylinder under the spout to catch the displaced water.
Carefully lower the object into the Eureka can.
(The object must be fully submerged without splashing.)
Collect the water displaced into the measuring cylinder and record its volume.
(This volume is equal to the volume of the object.)
Use the density formula again:
Tips for Accuracy for density
Ensure no air bubbles stick to the object.
Dry the object before weighing it.
Read volume at eye level (bottom of meniscus).
We are going to use a ray box, a lens, and a slit (this produces a narrow ray of light).
Ray boxes get hot, so it is important to switch them off when not being used.
We could also do this practical using a laser, but that can be more dangerous, so a ray box is safer.
First, we take a sheet of A3 paper and draw a straight line down the centre using a ruler.
We then use a protractor to draw a line at right angles; this is the normal, so we label this N.
We now place a glass block against the first line so the normal is near the centre of the block.
Now we draw around the glass block.
At this point, we need to turn off all lights in the room.
Next, we use the ray box to direct a ray of light so it hits the block at the normal; this is the incident ray.
The angle between the incident ray and the normal is the angle of incidence.
Now adjust the ray box to change the angle of incidence.
At a certain angle, we can see a ray reflect from the surface of the block.
We can also see another ray leaving the block from the opposite side; this is the transmitted ray.
We now mark the path of the incident ray and the reflected ray with crosses.
We also mark the path of the transmitted ray.
Now we turn on the room lights and switch off the ray box.
Finally, we remove the glass block.
Infrared
- We can use a Leslie’s cube to see how much infrared radiation is emitted from different substances
- A Leslie’s cube has four different surfaces
- There is a shiny metallic surface, a white surface, a shiny black surface and a matt black surface (matt means not shiny)
- First we fill a Leslie’s cube with hot water
- We then point an infrared radiation detector at each of the four surfaces and record the amount of infrared radiation emitted
- It is very important that we keep the same distance between the Leslie’s cube and the infrared red detector
- This makes the measurements repeatable
- The matt black surface should emits the most infrared radiation, followed by the shiny black then white then shiny metallic
- If we do not have a infrared detector we can use a thermometer with the bulb painted in black
- However the resolution of the thermometer is less than the infrared detector
- The resolution is the smallest change that can be detected
- We may not be able to detect a large difference between the surfaces using a thermometer
- Wheras the infrared detector is more likely to detect a difference
How to measure the absorbance of infrared by different surfaces
- We have a infrared heater on either side and two metal plates on each side
- One plate has been painted with shiny metallic painted with matt black paint
- On the other side we have used Vaseline to attach a drawing pin
- We now switch on the heater and start timing
- The temperature of the metal plates increases as they absorb infrared
- We record the time it takes for the Vaseline to melt and the drawing pins to fall off
- What we find is that the drawing pin of the matt black plate falls of first
- That is because matt black surfaces absorb mor infrared than shiny metallic surfaces
- Matt surfaces are much better at emitting and absorbing infrared radiation than shiny metallic surfaces
- Infrared tends be reflected from shiny metallic surfaces instead
