2330635
Descripción
Fichas por Holly Bamford, actualizado hace más de 1 año
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Creado por Holly Bamford
hace más de 9 años
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| Pregunta | Respuesta |
| What do we use X-rays in hospitals for? | to make images and C.T. scans to destroy tumours at or near the body surface |
| Why are X-rays dangerous? | they ionise substances they pass through, which can damage them. |
| What can we say about the absorption of X-rays when they pass through the body? | X-rays are absorbed more by bones and teeth than by soft tissues |
| What is a C.T. scan? | C.T. scans distinguish between different types of soft tissue as well as bones and teeth |
| What are ultrasound waves? | sound waves of a frequency above 20 000 Hz |
| What are ultrasound waves used for in medicine? | Ultrasonic scanning Destruction of kidney stones |
| Why is an ultrasound scan safer than a X-ray? | It is non-ionising. |
| What do we mean by the refractive index of a transparent substance? | It is a measure of how much a substance can refract a light ray |
| How can we calculate the refractive index? | sin (i) ____ sin (r) |
| What do we mean by the critical angle of a substance? | the angle of incidence of a light ray in a transparent substance that produces refraction along a boundary |
| How is the critical angle related to the refractive index of the substance? | 1 ----- Sin (c) |
| What do we mean by total internal reflection? | when the angle of incidence is greater than the critical angle. |
| What do doctors use an endoscope for? | to see inside the body directly |
| What is a converging lens? | Convex- focuses parallel rays to a point (principal focus) |
| What is a diverging lens? | Concave- makes parallel rays spread out as if they came from a principle focus. |
| What is a real image? | Is formed if the the object is further away than the principal focus |
| What is a virtual image? | Formed if the object is nearer to the lens than the principal focus |
| What do we mean by magnification? | image height ------------- object height |
| How can we find the position and nature of an image formed by a lens? | a ray diagram can be drawn |
| How does the eye work? | Light is focused on to the retina by the cornea and the eye lens, which is a variable focus lens |
| What is the range of vision of the human eye? | 25 cm to infinity |
| What do we mean by the power of a lens? | P=1/focal length in meters (f) |
| What is short sight and how do we correct it? | Can only see near objects clearly. Use a diverging lens |
| What is long sight and how do we fix it? | Can only see distant objects clearly Use a converging lens |
| Why is the refractive index of glass important in making spectacle lenses? | The higher the refractive index the thinner and flatter the lens can be |
| what does the moment of a force measure? | The turning affect of the force of an object |
| How do we calculate the moment of a force? | F about a pivot = F x d were d is the perpendicular distance from the line of action of the force to the pivot. |
| How can we increase the moment of a force? | increase f or increase d |
| What is the centre of mass of an object? | Were mass may be thought to be concentrated |
| What can we say about the centre of mass of an object that is suspended from a fixed point? | When it is suspended in equilibrium it's centre of mass is directly below the point of suspension |
| What can we say about the centre of mass of a symmetrical object? | Th centre of mass is along the axis of symmetry. |
| If an object is in equilibrium the sum of the anticlockwise movements about any point equal...? | the sum of any clockwise movement about a point |
| What can be done to increase the stability of an object? | increase the base width and lower the centre of mass |
| What will make a body topple over? | if the line of action is outside it's base |
| An object topples over if...? | the resultant moment about i's turning point is not zero |
| What do we mean by pressure? | It is force divided by the area on which the force acts (pascal (Pa)) |
| What can we say about the pressure in a liquid? | it acts equally in all directions |
| How is pressure transmitted in a hydraulic system? | Liquid is virtually incompressible, so the pressure in a hydraulics system is transmitted through the oil |
| What is centripetal force? | An object moving in a circle is acted on by centripetal force |
| What affects the time period of a pendulum? | It's length |
| How do you measure the time period of a pendulum accurately? | Measure the average time for 20 oscillations and divide it by 20 |
| What do we mean by magnetic field lines? | The line along which a plotting compass points |
| How do we make electromagnets? | A coil of insulated wire wrapped round an iron core |
| What are electromagnets used for? | scrapyard cranes circuit breakers electric bells relays |
| What is the motor effect? | a force can act on a wire in a magnetic field when we pass a current through the wire |
| In the motor effect the force is...? | -increased if the current of magnetic field strength is increased -at right angle to the direction of the magnetic field -is reversed if the current of magnetic field strength is reversed |
| How is the motor effect used to make objects move? | an electric motor has a coil which turns when a current is passed through it |
| What is electromagnetic induction? | the process of creating potential difference using a magnetic field |
| how can a magnet be used to induce potential difference across the ends of the conductor? | If a conductor cuts the line of a magnetic field a potential difference is induced across the ends of the conductor |
| How can potential difference be induced if a electromagnet is used instead of a magnet? | It has to be turned on to induce a potential difference |
| Why do transformers only work with ac? | because a changing magnetic field is nececssary to induce ac in the secondary coil |
| What is the core of a transformer made from? | an iron ore unless it is a switch mode transformer which has a ferrite core |
| How does a switch mode transformer differ from an ordinary transformer? | it is lighter and smaller it operates on a high frequency |
| Why are transformers used on the national grid? | to step potential difference up or down |
| What is the transformer equation? | |
| What is the difference between a step down and step up transformer? | for a step up transformer N s is less than N p For a step up transformer N s is greater than N p |
| What can we say about a transformer which is 100% efficient? | Vp*Ip =Vs*Is where Ip=primary current Is=secondary current |
| How do we use physics in hospitals? | We use physics whenever: blood pressure or temp. is measured ECG recordings are taken endoscopes are used scanners are used |
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