P3 Revision Pack (Please keep this pack with you)

Transcription

1 Name: P3 Revision Pack (Please keep this pack with you) Follow all the steps below... 1) Learn units for the equation sheet (included) 2) Practice all the maths questions using the equation sheet (40% of paper is MATHS!) Maths and Science Skills Questions Standard Questions Higher Questions 3) Practice Quiz short answer questions (included in this pack) 4) Practice QWC questions long answer questions (included in this pack) 5) Practice all the Popplet questions P3.1 Medical applications of Physics P3.2 Using physics to make things work P3.3 Keeping things moving Standard Questions Higher Questions Standard Questions Higher Questions Standard Questions Higher Questions Our Predictions: EVERYTHING!!!! Learn the units! MATHS! Don t forget to convert units, rearrange equations, significant figures, standard form, combining equations, using answers from previous question to answer next question etc. Ultrasound and X-ray, how they work, dangers, advantages and disadvantages, comparison Electromagnets, e.g. how it works (possible 6 marker) P3.1! Moments Transformers How to calculate the centre of mass in a regular object Stability Structure of the eye, name the parts and functions, long and short sightedness Ray diagrams

2 EQUATION SHEET: SAME AS P2! You need to remember the units

3 PRACTICE QUIZ 1 Advantages & Disadvantages of CT scanning (X- Rays) 2 Properties & Uses of ultrasound : Scan produce a picture / distinguish between soft tissue & bone : X-rays ionise tissue & can cause DNA to mutate Above 20kHz Depth = ½ * speed * time Used in pre-natal scanning 3 What is the refractive index? Measure of how much a substance can refract light n=sin i / sin r 4 How do fibre optics work? Light is Totally Internally Reflected (TIR) Light hits the side at an angle > critical angle n = 1 / sin c 5 Properties of lenses Converging (convex) or Diverging (concave) Magnification = image height / object height Image is virtual if it is not formed from real rays Images may be inverted or erect (upright) Materials with higher refractive index can be thinner for same refraction (e.g. glasses) 6 Rays on a converging lens diagram Through centre undeviated Parallel to PA goes through FP Through FP comes out parallel to PA 7 Rays on a diverging lens diagram Through centre undeviated Parallel to PA out as if it came from FP Towards far FP come out parallel to PA Object > 2FL: Diminished, Inverted, Real 8 Object at 2FL: Same size, Inverted, Real How is the image from a converging lens affected Object between FL and 2FL: Magnified, Inverted, Real by the position of the object? Object at FL: No clear image Object at less than FL: Magnified, Upright, Virtual (magnifying glass) 9 The eye: Parts & Functions Iris (muscle controlling the amount of light) Cornea (transparent protective layer) Pupil (hole formed by the iris) Ciliary muscles (change thickness of the lens) Lens (focus light onto the retina) Retina (light sensitive coating on the back of the eye) Blind spot (part of the retina which is not sensitive to light) Optic nerve (carries nerve impulses to the brain) 10 Eye Vision properties Near point 25cm. Far point infinity Power (Dipotres) = 1/focal length (m) 11 How are eye defects caused? Short sightedness: Lens too thick (diverging glasses needed) Long sightedness: Lens too thin (converging glasses needed) 12 Compare the eye & the camera Eye focus is variable / Camera it is fixed Eye focus adjustment through muscles / Camera through moving the lens Images are both real and diminished Eye image detection on the retina / Camera on film or CCD (digital) Eye brightness control via iris+pupil / Camera via adjustment of aperture 13 Moments Force x Perpendicular distance from pivot Measured in Nm In Equilibrium CW and ACW moments are balance (F1d1=F2d2) 14 Centre of mass Can be found by suspending and dropping a vertical plumbline. Draw a line then rehang and repeat. COM is where the lines cross Point at which all the mass can be said to act 15 Stability Object topples when COM (line of action) is no longer above the base (resultant moment)

4 Increase stability by widening base or lowering COM 16 How do hydraulics work? Pressure in liquids is the same everywhere Liquids are virtually incompressible In a piston system the pressure at both pistons is the same 17 How is pressure calculated? Pressure measured in Pa (N/m 2 ) Pressure = F/A (so F1/A1 = F2/A2) 18 What factors affect centripetal motion? Mass of the object Velocity of the object Radius of the orbit 19 What direction is the acceleration in circular Towards the centre (provided by a force which acts in that motion? direction usually gravity or tension) 20 Properties of a pendulum Velocity proportional to distance from the midpoint Time period = 1/frequency (Hz) Energy interconverted between kinetic and gravitational potential Energy slowly lost due to friction at the pivot point 21 How do electromagnets work? Moving current in a conductor creates a magnetic field Field affected by Core, Current, Coils 22 How does a speaker work? Moving current creates a magnetic field Interacts with the permanent magnet s field Cone attracts Direction of the force reversed when direction of the current is reversed (a.c.) 23 What is the motor effect? Moving current through a conductor in a magnetic field creates motion Split-ring commutator required for DC current Direction of the force determined through Left Hand Rule (First = Field, Second = Current, Thumb = Motion) 24 What is electromagnetic induction? Moving magnet through a coil of wire induces a potential difference in that wire Also possible to move a coil of wire through a magnetic field 25 How is the amount of induced PD affected? Speed of movement / strength of magnet / number of coils affects the induced PD 26 How does a transformer work? AC produces alternating magnetic field Field lines pass through the second coil Changing field lines induce PD in the second coil Requires AC Iron core (plates laminated to reduce heating energy losses) 27 How does the number of coils affect the type of transformer? 28 What is a switch-mode transformer? 29 How is the voltage determined? More coils on the side with the higher PD Step-up has more coils on the secondary side Step-down has more coils on the primary side Operates at very high frequency (50kHz) Ferrite core (lighter than iron core) Uses little power when not connected to a secondary device Voltage determined by the ratio of the coils Tp/Vp = Ts/Vs Also VpIp=VsIs [for 100% efficient transformer] 30 Why do we use transformers? Need high PD in the power lines (and so reduce current) This reduces energy losses due to heating

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23 QWC 6 MARK QUESTIONS Q1. Compare the medical uses of ultrasound and X-rays. Your answer should include the risks, if any, and precautions, if any, associated with the use of ultrasound and X-rays. KEY POINTS TO INCLUDE IN ANSWER: Medical use of X-rays Detecting bone fractures Detecting dental problems Killing cancer cells CT scanning. Risks with X-rays X-rays pose a risk / danger / hazard X-rays cause ionisation / damage to cells mutate cells / cause mutations / increase chances of mutations turn cells cancerous / produce abnormal growths / produce rapidly growing cells kill cells (may) cause cancer Operator precautions with X-rays The X-ray operator should go behind a (metal / glass) screen / leave the room when making an X-ray / wear a lead lined apron appropriate precautions for the patient include limiting the total exposure / dose (in one year) Medical use of ultrasound Pre-natal scanning Imaging (a named body part) Removal / destruction of kidney / gall stones Removing plaque from teeth repair of damaged tissue / muscle Risks with ultrasound Ultrasound poses no risk / danger / hazard (to the user / patient) accept ultrasound is safer than using X-rays Ultrasound is not ionising Ultrasound does not damage (human) cells Precautions with ultrasound The operator needs to take no precautions when making an ultrasound scan

24 Q2. The student taped a 100 g mass to a metre rule. She set up the apparatus as shown in the diagram. She suspended the metre rule from a nail through a hole close to one end, so she could use the metre rule as a pendulum. The distance d is the distance between the nail and the 100 g mass. The student carried out an investigation to find out how the time period of the pendulum varies with d. Some of her results are shown in the table. d in cm First test Time for 10 swings in seconds Second test Third test Mean value Mean time for 1 swing in seconds Describe how the student would carry out the investigation to get the results in the table in part. You should include: any other apparatus required how she should use the apparatus how she could make it a fair test a risk assessment how she could make her results as accurate as possible. KEY POINTS TO INCLUDE IN ANSWER: additional apparatus stopwatch use of apparatus measure from hole to centre of the mass pull rule to one side, release time for 10 swings and repeat divide mean by 10 change position of mass and repeat fair test keep other factors constant time to same point on swing risk assessment injury from sharp nail stand topple over rule hit someone accuracy take more than 4 values of d estimate position of centre of slotted mass small amplitudes discard anomalous results use of fiducial marker

25 Q3. Lasers can be used to correct a visual defect by changing the shape of the cornea. A knife is used to cut a flap in the cornea. The laser vaporises a portion of the cornea and permanently changes its shape. The flap is then replaced. Most patients are back at work within a week. Driving may be unsafe for one to two weeks. Tinted glasses with ultraviolet protection are needed when out in the sun for the first three months. Many people in their mid-40s need reading glasses. This is because the eye lens becomes less flexible with age. Laser surgery cannot cure this. Laser surgery for both eyes costs A pair of glasses costs 250. Describe the advantages and disadvantages of: having laser surgery to correct visual defects wearing glasses to correct visual defects. KEY POINTS TO INCLUDE IN ANSWER: laser surgery advantages: o appearance o permanent effect o no glasses which need changing disadvantages: o risks associated with surgery o large cost o not able to drive etc straightaway o (still) might need glasses for reading wearing glasses advantages: o able to function straightaway o any problems easy to sort out disadvantages: o easily broken o easily lost o need changing o overall cost might be greater if several changes in vision o might eventually need two pairs of glasses Q4. There are two types of traditional transformer; step-up and step-down. Describe the similarities and differences between a step-up transformer and a step-down transformer. You should include details of: construction, including materials used the effect the transformer has on the input potential difference (p.d.). KEY POINTS TO INCLUDE IN ANSWER: a laminated core core is made from a magnetic material / iron 2 coils the coils are made from an electrical conductor / copper the coils are covered in plastic / insulation the coils are (usually) on opposite sides step-up transformer has more turns on secondary coil than (its) primary (or vice versa) step-down transformer has fewer turns on secondary coil than (its) primary (or vice versa) step-up transformer, the output p.d. is greater (than the input p.d.) step-down transformer, the output p.d. is lower (than the input p.d.)

26 Q5. Figure 1 shows a sheet of card. Describe how to find the centre of mass of this sheet of card. Figure 1 KEY POINTS TO INCLUDE IN ANSWER: suspend shape from a point / pivot / pin attach pendulum (bob) / plumb line to point of suspension draw (vertical) line on card where string rests suspend card from another point and draw (a second vertical) line on card where string rests where two lines cross = centre of mass Q6.Ultrasound and X-rays are waves used in hospitals to create images of the inside of the human body. To produce the images below, the waves must enter the human body. Describe the features of ultrasound and X-rays, and what happens to each type of wave after it has entered the human body. KEY POINTS TO INCLUDE IN ANSWER: Description of an X-ray X-rays are electromagnetic waves / part of the electromagnetic spectrum X-rays are (very) high frequency (waves) through a vacuum / at the speed of light X-rays are (very) high energy (waves) X-rays have a (very) short wavelength Wavelength (of X-rays) is of a similar size to (the diameter of) an atom X-rays are a transverse wave X-rays are ionising radiation Description of ultrasound ultrasound has a frequency above (hertz) ultrasound is above / beyond the human (upper) limit (of hearing) ultrasound is a longitudinal wave correct description acceptable oscillations / vibrations (of particles) are parallel (in same direction) to direction of energy transfer Statement(s) as to what happens to X-rays inside the human body: X-rays are absorbed by bone X-rays travel through / are transmitted by tissue / skin Statement as to what happens to ultrasound inside body: ultrasound is (partially) reflected at / when it meets a boundary between two different media travel at different speeds through different media

27 Q7. The diagrams show a relay switch and how it is used in a car ignition circuit. Turning the ignition key closes the ignition switch. Explain how this causes the starter motor to operate. KEY POINTS TO INCLUDE IN ANSWER: current flows through the coil / electromagnet magnetic field produced accept electromagnet switches on (short side of) iron bar attracted to electromagnet contacts pushed together (by iron bar) starter motor circuit completed current flows through starter motor Q8. A current flowing in a coil produces a magnetic field in the core. Explain how an alternating input can produce an alternating output of a higher potential difference. KEY POINTS TO INCLUDE IN ANSWER: the magnetic field (in the iron core) is changing / alternating / varying the magnetic field links with the secondary / other coil a potential difference is induced in the other coil the potential difference induced in the other coil is alternating / changing the number of turns on the output is greater than the number on the input the turns ratio determines the particular value of the output voltage / potential difference

28 Q9. Susan has a case with wheels. When she packs this case, she puts the heaviest items at the end where the wheels are. This means that the heaviest items are less likely to crush the other contents and it helps her to find things when she opens the case. Explain another advantage of packing her case in this way. KEY POINTS TO INCLUDE IN ANSWER: lower centre of mass / gravity more stable less likely to fall over the turning effect / moment (of the weight of case) is less so less effort is needed to hold the case so the pull on her arm is less Q10. Circuit breakers help to make the electricity supply in homes safer. A circuit breaker is an automatic safety switch. It cuts off the current if it gets too big. Describe, in as much detail as you can, how this circuit breaker works. KEY POINTS TO INCLUDE IN ANSWER: bolt out > plunger up > switch off / circuit broken high current flows electromagnet is stronger the iron bolt is pulled out the plastic plunger moves up the switch is lifted / open / off no current flowing to re-set the plunger must be pushed down