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revision HELP AS physics Edexcel

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    i read a few things in the physics specification for AS Edexcel which i have no clue what their about , and im really worried pleasse HELP me !

    what are the basic info i need to know for the following -

    1)explore and explain how a pulse-echo technique can provide details of the position and/or speed of an object and describe applications that use this technique

    2)explain qualitatively how the movement of a source of sound or light relative to an observer/detector gives rise to a shift in frequency (Doppler effect) and explore applications that use this effect

    3)explain how the amount of detail in a scan may be limited by the wavelength of the radiation or by the duration of pulses

    4) discuss the social and ethical issues that need to be considered, eg, when developing and trialling new medical techniques on patients or when funding a space mission

    5)demonstrate an understanding of how ICT may be used to obtain current-potential difference graphs, including non-ohmic materials and compare this with traditional techniques in terms of reliability and validity of data

    im a private candidate, i dont kno anyone doing the same board as i am, PLEASEEE HELP !!!!:confused:
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    I'll start by saying I got 118/120 for unit 1, and 102/120 for unit 2, although I didn't achieve these first time around.

    These are two tricky exams, and dw I am doing Edexcel, I get so frustrated at some of the stuff they throw into these exams!

    Lets work through what you wanted... shall we?

    mmmm.....kay. Pulse echo is used for baby scans, u know this, they may ask why... because it isn't dangerous of course. THIS IS KEY: The difference in density at any boundary where a reflection occurs dictates how strong the reflection is. This is how the pulse echo creates the picture, as it reflects off different boundaries to create stronger image in certain places.

    Secondly Doppler effect : Shift in frequency is proportional to the relative speed between the source and the observer.

    Oh f**k this, I got dinner so I'm gna go, can't actually remember why i'm helping people with exams I've already done...:confused: my mums making Pizza's YAY !

    Holler at me if you need anything specific, i.e. exam questions I can help you with.

    google image search: RED RUFFED LEMURS sooooo cute !
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    (Original post by omaimah93)
    i read a few things in the physics specification for AS Edexcel which i have no clue what their about , and im really worried pleasse HELP me !

    what are the basic info i need to know for the following -

    1)explore and explain how a pulse-echo technique can provide details of the position and/or speed of an object and describe applications that use this technique

    2)explain qualitatively how the movement of a source of sound or light relative to an observer/detector gives rise to a shift in frequency (Doppler effect) and explore applications that use this effect

    3)explain how the amount of detail in a scan may be limited by the wavelength of the radiation or by the duration of pulses

    4) discuss the social and ethical issues that need to be considered, eg, when developing and trialling new medical techniques on patients or when funding a space mission

    5)demonstrate an understanding of how ICT may be used to obtain current-potential difference graphs, including non-ohmic materials and compare this with traditional techniques in terms of reliability and validity of data

    im a private candidate, i dont kno anyone doing the same board as i am, PLEASEEE HELP !!!!:confused:
    Hey I am on a gap year so have completed both AS and A2 Physics so I will try to help you the best I can.

    1) Basically a pulse echo technique refers to sending out a sound wave (usually ultrasound) to an object an unknown distance away.

    For example:

    - Imagine that you are on a boat and you want to see how deep the water is that you are in.

    - You would send out an ultrasound pulse into the water. This pulse would eventually hit the bottom and reflect back up towards the boat.

    - A detector on your boat would then record the time taken from which the impulse was sent for it to return.

    - You already know the speed of sound (approx. 340ms-1) you have then just found out the time taken for the pulse to return.

    - Using SPEED=DISTANCE/TIME you can work out your distance.

    For example, it took 5s for the pulse to return.

    Speed= Distance/Time

    Therefore Distance=SpeedXTime

    Distance=340X5

    Distance=1700m

    BUT A VERY IMPORTANT THING TO REMEMBER IS THAT THIS IS THE DISTANCE THERE AND BACK AS THE TIME RECORDED WAS FOR THE PULSE TO TRAVEL TO THE BED AND BACK.

    ALL YOU NEED TO DO IS DIVIDE BY 2

    SO DISTANCE=850m


    This technique is used for the following:-
    - Measuring the distance of sholes of fish in the sea.
    - Measuring the distance of stars using a radio telescope
    - Radar (Speeding) Guns that are used by the police.

    To work out the speed of a moving vehicle a radar gun will send out an initial pulse and measure the distance of the vehicle. It will send out a second pulse several seconds later and measure the distance again. Remember this uses radio waves and not sound waves so would have a speed of 3x10^8ms-1

    For example:-

    - A radar gun sends out an impulse and finds that a car is 50m away.

    - A second impulse is sent out 2s later and the car is now 100m away.

    - So in 2s it has travelled 50m.

    - So as SPEED=DISTANCE/TIME

    - SPEED=50/2

    - So the speed is 25ms-1


    2) Imagine that you are standing on a pavement and a police car is approaching you. As the police car gets closer the pitch of its siren gets higher. As it moves away the pitch gets lower.

    Click image for larger version. 

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    As the siren approaches you the sound waves get bunched up and are closer together. In other words they are of higher frequency. As the siren moves away from you the sound waves spread further apart and are of lower frequency.

    Hopefully the diagram should help you with that.

    Other times we see the Doppler Effect are when we are observing distant galaxies. You may have heard of the term red shift. This is down to the Doppler Effect and gives astronomers evidence that our universe is expanding. If a light emitting object is moving towards a stationary observer, the light waves will bunch up and have a shorter wavelength. In other words it will be shifted to the blue end of the spectrum (blue-shift). If a light emitting object is moving away from a stationary observer, the light waves will spread out and have a longer wavelength. In other words it will be shifted to the red end of the spectrum (red-shift).

    Click image for larger version. 

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    3) What you need to remember with this question is that the shorter the wavelength of something the less diffraction they undergo. Therefore the shorter the wavelength of sound, the less the waves spread out when they travel. This means that shorter wavelengths can map tissues of different interfaces more precisely producing a clearer image.

    Ultrasound images also use short pulses (usually lasting a few microseconds) this prevents reflections from nearby interfaces from reaching the transducer before the pulse has finished.

    The gap between each pulse however must be quite long (usually at least 1 millisecond). This is to make sure that all the reflected waves from one pulse return back to the transducer before the next pulse is emitted.

    4) For this question all you need to remember is the acronym SEES

    Safety

    Will it cause more harm than good? e.g. an X-ray couls how up a medical problem, but are known to damage cells. Long exposure can cause cancer

    Ethical

    Is it morally right? e.g. ultrasound scans can reveal the gender of a foetus. However this may lead to unnecessary termination

    Expense

    Do the benefits outweigh the cost? e.g. MRI scanners can produce a much clearer image than ultrasound and are safer than X-Rays but are much more expensive

    Social

    Will it benefit society or adversely affect people? e.g. doctors can scan foetuses for birth problems such as abnormal growth which they could put right. Alternatively this could lead to termination

    Hope this helps if you need any more help let me know

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