PPP Mistakes Flashcards
(29 cards)
A massive ball is released from rest above the ground.
According to a student, the principle of conservation of momentum is violated because the ball gains momentum as it falls.
Explain why the students observation is incomplete and discuss how momentum is conserved in this situation.
Earth is mentioned as an integral part of the system
The earth has equal and opposite momentum to the falling ball so momentum is conserved
Explain why the intensity of the wave changes as the distance x increases
As the wave spreads out the amplitude decreases
Intensity is proportional to amplitude ^2 and therefore intensity decreases
Describe how the wavelength of the progressive wave on the stretched wire depends on frequency of vibration of the wire
Speed / v of the progressive wave is the same
Wavelength decreases as frequency increases
Wavelength is halved when f is doubled
Explain without doing any calculations how you can determine the percentage uncertainty
Draw a worst-fit line and determine gradient h
% uncertainty = (1/2 range divide average h) x 100
The brakes of the train are applied with the same average braking force.
State and explain the distance travelled from when the driver applies the brakes to when the car stops
KE is transferred to GPE
Smaller distance because larger opposing forces
Describe how a metre rule and a stopwatch can be used to determine a final velocity v of the trolley at the bottom of the ramp
Distance/displacement/length measured using a metre rule and time measured using a stopwatch
Use v=root2gh
By considering the forces acting on the tube on fig 23.2 2018 breadth
Upthrust is constant up to 60s
Constant gradient before 60s because upthrust increases at a constant rate
After t=60s eventually the upthust is constant because tube is fully submerged.
F=upthrust - weight
Explain why the receiver now detects microwaves
This is because diffraction occurs at the narrow slits
The is because the wavelength is similar
Compare the speed, frequency and wavelength of light in air and in water
Speed of light is less in water
Frequency is the same in both
Wavelength is smaller in water
Describe with the aid of a ray diagram how an experiment can be conducted to accurately determine the critical angle for light within the glass block and hence the refractive index of the glass.
Use a protractor to measure angle
Refractive index determined using n = 1/sinC
Draw diagram
Explain why the detected signals behave like this way
Electric field perpendicular to the direction of motion
At 0 to 180 the grille blocks all the polarised waves and at 90 the grille allows all the microwaves to pass
Describe how you can use a ray-box together with other equipment available in laboratory to accurately determine refractive index of the plastic block
Measure angle using protractor
Plot sini/sinr graph
Use narrow beam of light for ray box
Refractive index = sini/sinr
Explain how the graph now appears from the time the ball is released to the time it hits the surface
Line will curve and line will end with lower maximum final velocity
What is threshold wavelength
The maximum wavelength for electrons to be emitted
Describe how you would carry out an experiment to accurately determine the threshold voltage of an LED in brightly lit laboratory
Increase the pd until the led is just lit
To observe the light from the led use a tube
Describe and explain how the angles p and q will change. In your answer, include the terms critical angle.
As p increases q increases
If light at angles greater than the critical angle then total IR occurs
SinC=1/n
When i is 60 there is no angle q
Describe how the addition of two velocities is different to the addition of two masses
Mass is a scalar quantity and velocity is a vector quantity
Addition of velocities depends on direction
Describe how you can use instruments available in a physics laboratory to determine the pressure exerted by the cylinder on the table. State how you would make your results as precise as possible
Pressure = Weight of cylinder/area
Weight of cylinder measured using a newton meter
Area is determined by measuring the diameter using a ruler then do piR^2
Use micrometer or vernier calliper to reduce % uncertainty
What is the similarity and difference between emf and Pd
Same units
Emf is when work is being done on the electrons. PD is when work is being done by the electrons.
Describe how the wavelength of the transverse wave on the stretched cord can be determined
The wavelength is twice the length of the cord
What is the area under a force - extension graph
Elastic potential energy
Describe how the student can use a graph and additional measuring instrument to accurately determine p
Measure diameter using micrometer
Gradient of line multiplied by CSA gives p
A=pid^2/4
What is the wavelength and use for radiowave
10^-1 - 10^4
Television
What is the wavelength and use for microwave
10^-4 - 10^-1
Mobile Phones
