Exam Questions (Redos, Techniques, Facts) Flashcards
Questions wrong from question packs that need repeating
In an experiment which involved measuring time, a student used a stopwatch - describe how different apparatus could be used to measure the time so that the % uncertainty is reduced
Either use a light gate and data logger for a more accurate determination of time
Or a video camera which can be analysed frame by frame
Describe one safety precaution when carrying out the speed of stationary wave on string practical
Wear suitable footwear (to protect from falling masses)
Wear safety glasses (in case teh string breaks)
When using a micrometer, give 1 technique for measuring stuff well
Look at the micrometer from different orientations along the wire
As the wire diameter may not be uniform
OR
Check for 0 error
As zero error reduces the accuracy of measurement
When describing how a vibrating string causes pressure variations in the air: how do you describe how the molecules oscillate?
Molecules are displaced from equilibrium positions
Never say antibodies have larger amplitude (when describing standing waves) instead say ____amplitude
Maximum
Explain why waves need to be coherent to produce a standing wave
Coherent means the waves have a constant phase relationship
If the relationship is not constant, a point could be sometimes constructive and sometimes destructive
If the number of slits per mm in the diffraction grating increases, does d increase or decrease?
d = the slit separation
So it decreases
REMEMBER WHAT when writing your final answer
Units
What do you do to ensure accuracy of an experiment (increasing the likelihood of accuracy)
Decrease % uncertainty
(By increasing measumrent size or increasing resolution)
Things with longer ___ diffract more
Wavelengths
What is the unit of sin theta - how should you write the units for sin theta?
Sin (theta/little zero for degrees)
How can you check whether a diffraction grating with a certain spacing is appropriate to measure d sin theta = n lambda?
There should be a significant difference in the angles for each of the maximas
- diffraction occurs when light is reflected from the CD surface
- each ring on the CD acts as a diffraction centre scattering light in all directions
- interference occurs
- in directions in which there is a phase difference equal to an even multiply of pi radians (or a who,e number of wavelengths) there is constructive interference
- white light is a range of wavelengths
- each wavelength of light reinforces in a different direction which explains why a spectrum is seen
Criticise these results
Inconsistent number of decimal places for resistance (resistance should be to 3dp)
Inconsistent intervals in temperature (large jump in temperature from 38 to 55)
Should you include units for calculations of gradients?
Yes
Give 3 things you could do to improve the accuracy of measumrents of your (y intercept) or (gradient)?
(Things in brackets would be replaced with the specific context of the question)
- take a measurement at 0 (with units) to measure (y intercept) accurately
- take (resistance) measurements for smaller increments (of temperature) - to improve accuracy of gradient
- use a digital (thermometer) - to avoid parallax error
- take (resistance) measurements for a wider range of (temperatures) - wider range of independent variable - to improve the accuracy of the gradient
What two errors should you be careful to avoid when using a micrometer or vernier calliper/two ways of making the experiment more accurate
- check for zero error
- take readings in different orientations/positions
Describe how a student can accurately determine the radius of the first bring ring/distance to maxima point of a diffraction pattern
- use vernier callipers
- measure the diameter of teh first ring and divide by 2 (or distance from first order maxima on left to maxima on right and divide by 2)
- measure in multiple orientations and calculate the mean
- measure to the middle/brightest part of the ring
Explain how a diffraction pattern (showing concentric bright rings) gives evidence for the wave nature of electrons
- diffraction is a wave property
- the diffraction pattern is evidence the electrons have interfered
When rearranging an equation into straight line form to explain why the line of best fit is a straight line what is it important to state
- that (the variables which are constants) are constants
Explain how you could use a vernier callipers to measure the diameter of a coin accurately
- measure multiple coins / multiple positions/orientations on the same coin
Mean diameter calculated - check and correct for zero error of the measuring device
Explain the variation of resistance with potential difference for the filament bulb in terms of particle behaviour
- as pd increases the energy of electrons increases
- so there is greater energy transfer in collisions with lattice ions
- increasing the temperature of the metal/filament/ions
- amplitude of vibrations of lattice ions increases
- collision rate between lattice ions and electrons increases
- due to the increase in resistance, the ratio of I/V decreases
NOTE the energy transfer being greater is a significant part of the answer!
Add the missing sentence to this answer
Thermistor resistance as a proportion of total resistance decreases
Discuss the suitability of each circuit to collect the data
(Remember to write a statement in agreement if it asks you to discuss!)
- both circuits are suitable as they allow readings of pd/current for the lamp
- for circuit 1 the minimum pd across the lamp is 0V when the slider is on the left
- for circuit 1 the maximum pd across the lamp is the supply pd (when the slider is at the right)
- for circuit 2 adjusting the resistor changes the circuit resistance (so the current is varied)
- so for circuit 2 the minimum pd depends upon the resistance of the variable resistor
- circuit 1 is better because it allows a bigger range, and allows pds down to 0V to be used
- the battery has internal resistance
- there is a pd across the internal resistance of the battery (lost volts)
- terminal pd is less than emf
How should you edit the last sentence (instead of saying overheat) to get full marks on this question?
It reduces the life of the remaining bulbs
To determine cross sectional area of a wire what equipment should you use
A micrometer
You need a wire to make a 3 A fuse
If the actual maximum current of a fuse wire before it breaks is less than 3A does that make it suitable for use or not?
Yes
What is the limit on pulse length and distance for pulse echo technique
- pulse length needs to be less than half distance / half pulse length needs to be less than distance
- half wavelength needs to be less than distance
Or wavelength needs to be less than half distance
Explain why birds emit pulses with shorter time intervals between them when they are close to an obstacle than when they are further from an obstacle
- the birds needs to distinguish between received clicks, so one must be eceuved beckre the next is sent
- as the bird gets closer to an obstacle more frequent updates on the position are enquired
Explain how pulse echo location for birds works
- they detect the reflection of their clicks
- the close an obstacle is the shorter the time interval between the clicks returning
What is the rule for the number of dp in calculated data from addition/subtraction?
Same number of dp as the limiting term in the raw data
Always say that there are 4 ____ OF RESULTS in a table rather than 4 results
SETS
Give the final % uncertainty to ___ significant figures
One to two
What is conservation of momentum?
Total momentum before a Collision is equal to the total momentum after a collision, provided no external force es act
Give a reason why the ultrasound is emitted in short pulses
So the reflected pulse returns before next pulse is transmitted
What is the rule for number of dp/sf of calculated data after division or multiplication of raw data
Same number of sf as the limiting term (minimum number in raw data)
What is the rule for number of dp/sf for addition/subtraction of raw data to make calculated data?
Number of dp of the limiting term (minimum number of dp in raw data)
How to measure diameter of a wire accurately
Use a micrometer , check for zero error first
Measure the diameter of the wire in at least 3 different positions and orientations along the wire and then take a mean
To reduce the effect of random error
Never leave % uncertainty to more than ___sig fig
2
How do you find total uncertainty in A^2 + D^2
When you are adding you use sum of absolute uncertainty of both
