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Description
Flashcards by Olly Howes, updated more than 1 year ago
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Created by Olly Howes
almost 9 years ago
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| Question | Answer |
| X-Rays | X-Rays are part of the electromagnet system and they have short wavelengths which are of the same order of magnitude as the diameter of atoms. They're used in hospitals to diagnose and treat conditions. They affect photographic film in the same way as light. They're detected using CCD's to form an image electronically. |
| X-Rays Continued | The advantages of X-Rays are that they are transmitted by healthy tissue and they're absorbed by metal and bone to produce shadow pictures. CT scans produce two and three dimensional images and they produce higher detail images, however, they increase the risk of radiation exposure to the patient. |
| Ultrasound | They are sound waves of frequencies greater than 20,000Hz. They are non-ionising electronic systems which produce electrical oscillations. These are used to generate ultrasonic waves. As the waves pass from medium or substance to another they're partially reflected at the boundary. They're used for pre-natal scans, ligament/muscle scans, and kidney scans. |
| Reflection of Light | When light strikes a reflective surface it will change direction. The normal line is constructed perpendicular to the reflecting surface at the point of incidence. In reflections the angle of incidence is the same as the angle of reflection. |
| Refraction of Light | This is when light crosses an interface and changes direction. No refraction happens when the lights enters at a 90 degree angle. The refractive index is a property of transparent media and can be determined by an equation. The RI of air is 1, water is 1.33 and glass is 1.5. |
| Converging and Diverging Lenses | A lens is a specially shaped piece of glass aiming to refract light to form an imagine at a certain point. Converging (convex) is thicker in the middle and refracts the light centrally. Diverging (concave) is thinner in the middle and refracts the light out, the image produced is not real. In lenses all light must go through a focal point. |
| Images Produced by Lenses | The size of an image produced by lenses depends on the distance between the object and lens. The image produced by a convex lens is real, inverted and smaller or magnified. The imagine produced by a concave lens is virtual and upright. |
| Structure of the Eye | |
| Eye Defects | There are two types of vision; long sight is caused by the eyeball being too short and the image is shown behind the cornea so you cannot see close objects well. Short sight is the opposite. Therefore lenses(glasses) are used to correct this. |
| Critical Angle | There are two special cases involving refraction of light; 1-The angle of refraction is equal to 90 degrees. The light travels on the boundary between glass and air and the angle of incidence is then called the critical angle. 2-The angle of incidence is greater than the critical angle so total internal reflection takes place where no refraction occurs so no light escapes. |
| Lasers | This is a device that amplifies light to produce an intense, narrow beam. Laser stands for Light Amplification by Stimulated Emission of Radiation. They can be made by s, l and g. Modern devices are very compact. Lasers are used in eye surgery to repair damaged retinas and to remove diseased or damaged cells. |
| Centre of Mass | This is the point on an object which the whole mass is concentrated to so if you put your finger in the middle of paper it balances. To find the COM you can attach string to various points on an object and draw the lines of string on the object, the point at which they meet is the COM. Objects with wide bases have low centre of masses and are more stable. |
| The Pendulum | A mass at the end of a string that oscillates (swings) back and forth is an example of a pendulum. The no. of times the object swings back and forth every second gives the freq. of oscillation. |
| Moments | Forces can be used to turn objects about a pivot point. The turning effect of this force is called the moment. To increase a moment you can increase the force or the perpendicular distance. |
| Levers | A lever is a device that acts like a force or distance multiplier. E.g. doubling the length of a spanner to undo a wheel nut will either double the moment of the force for the same force applied OR allow half the force to be applied to maintain the same amount of force. The application of levers is numerous but two examples are lifting a wheelbarrow or opening a tin of paint with a screwdriver. |
| Law of Moments | When an object isn't turning there must be a balance between the total moments of the forces turning the object clockwise and anticlockwise. If a plank is pivoted at its COM and has a force on each side the following is used: force1 x distance1 = force2 x distance2 |
| Stability | An object will topple if the line of action of the force (e.g. weight) lies outside it's base. The weight of the object causes a turning effect which makes the object topple. DIAGRAM IN BOOK |
| Pressure | Pressure is a force that acts over a particular surface area. A force acting over a small area gives a larger than the same force acting over a bigger area. P = F / A |
| Hydraulic Systems | Liquids are virtually incompressible, and the pressure in a liquid is transmitted equally in all directions. This means that a force exerted at one point on a liquid will spread to other points in the liquid. The pressure in liquid can be used to work machinery, this is hydraulics. |
| Centripetal Force | Any object moving with a constant speed in a circular path is continuously accelerating towards the centre of the circle. When the velocity changes there is an associated acceleration. This is due to the direction of motion always changing. This resultant force causing acceleration is centripetal force. |
| Centripetal Force Continued | The force may be provided by friction (e.g. a car's wheels on the road as it turns) or tension (e.g. a conker spun on a string). The force needed to make an object perform in a circular motion increases by increasing the mass or speed of the object, or decreasing the radius of the circle. |
| The Motor Effect | When a current flows through a wire a magnetic field is produced around the wire. This electromagnet effect is used on cranes to lift iron/steel, circuit breakers, loudspeakers and electric belts. When a wire carrying a current is placed in an external magnetic field, the field around the wire interacts with the permanent magnetic field. This makes a force so the wire moves. |
| Flemings Left-hand Rule | The First finger point in the direction of the magnetic Field, the seCond finger points in the direction of the Current and the thuMb points in the direction of the Movement. |
| Electromagnetic Induction | This uses movement to produce a current. Generators use this effect to produce electricity. If a conducting wire or coil of wires is moved through a magnetic field a p.d. is induced across the ends of the wire. If the coil forms part of a complete circuit an electrical current is induced. If there's no movement, no current flows. |
| Potential Difference | The size of the potential difference (and the current) can be increased by increasing the speed of the movement of the magnet or coils, increasing the strength of the magnetic field or increasing the number of turns on the coil. |
| Transformers | These change the electrical energy from one p.d to another. They're made of two coils called the primary and secondary coils, wrapped around a soft iron core. An alternating p.d across the primary coil causes an alternating current to flow. This current creates a continuously changes magnetic field around the core which induces an alternating p.d across the ends of the secondary coil. |
| Step-up and Step-down Transformers | A step-up transformer has more turns in the secondary than the primary coil. The p.d across the secondary is therefore larger than the primary. A step-down transformer has fewer turns in the secondary than primary coil. So the effect is the opposite. These transformers are used in the national grid to ensure the efficient transmission of electricity. |
| Switch Mode Transformers | These are much lighter and smaller than traditional transformers and operate at a much higher frequency, often between 50kHz and 200kHz. They operate using the 50kHz mains supply. They use very little power when they're switched on as no load is applied. They're useful applications as chargers for mobile phones, digital cameras and computer laptops. |
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