exam Flashcards

Question

What is mass

Answer 1

Mass: amount of matter an object contains, and is a property | that ‘resists’ change in motion

Answer 2

Weight is the force of gravity acting on an object, measured in Newtons, and given by the formula:

Answer 3

𝑾𝒆𝒊𝒈𝒉𝒕 = 𝑴𝒂𝒔𝒔 × 𝑮𝒓𝒂𝒗𝒊𝒕y

Answer 4

Weights (and hence masses) may be compared using a balance

Answer 5

𝑫𝒆𝒏𝒔𝒊𝒕𝒚 = 𝑴𝒂𝒔𝒔/𝑽𝒐𝒍𝒖𝒎e

Answer 6

Density of a liquid: place measuring cylinder on a balance, fill measuring cylinder with the liquid. The change in mass is mass of liquid and volume is shown on the scale, then use formula.

Answer 7

Finding the volume: To find out volume of a regular object, use mathematical formula. To find out volume of an irregular object, put object into a measuring cylinder with water and the rise of water is the volume of the object Finding the mass: weigh object on a scale and use formula

Answer 8

The density of water is 1g/cm3 if an object has a greater density than that, then it will sink in water, and if the object’s density is less than that, then it will float in water

Answer 9

A force may produce a change in size and shape of a body, give an acceleration or deceleration or a change in direction depending on the direction of the force.

Answer 10

If there is no resultant force acting on a body, it either remains at rest or continues at constant speed in a straight line

Answer 11

Friction: the force between two surfaces which impedes motion and results in heating

Answer 12

Air resistance is a form of friction

Answer 13

Springs extend in proportion to load, as long as they are under their proportional limit.

Answer 14

Limit of proportionality: point at which load and extension are no longer proportional

Answer 15

Elastic limit: point at which the spring will not return to | its original shape after being stretched

Answer 16

``` 𝐿𝑜𝑎𝑑(𝑁) = 𝑆𝑝𝑟𝑖𝑛𝑔 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡 × 𝑒𝑥𝑡𝑒𝑛𝑠𝑖𝑜𝑛 𝑭 = 𝒌𝒆 ```

Answer 17

F=MA | 𝑭𝒐𝒓𝒄𝒆 = 𝑴𝒂𝒔𝒔 × 𝑨𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏

Answer 18

Force is measured in Newtons

Answer 19

1 Newton is the amount of force needed to give 1kg an | acceleration of 1m/s2

Answer 20

An object at steady speed in circular orbit is always accelerating as its direction is changing, but it gets no closer to the center

Answer 21

Centripetal force is the force acting towards the center of a circle. It is a force that is needed, not caused, by circular motion

Answer 22

Centrifugal force is the force acting away from the center of a circle. This is what makes a slingshot go outwards as you spin it. The centrifugal force is the reaction to the centripetal force. It has the same magnitude but opposite direction to centripetal force.

Answer 23

First law of motion: If no external for is acting on it, an object will, if stationary, remain stationary, and if moving, keep moving at a steady speed in the same straight line

Answer 24

Second law of motion: 𝑭 = 𝒎𝒂

Answer 25

Third law of motion: if object A exerts a force on object B, then object B will exert an equal but opposite force on object A

Answer 26

𝑴𝒐𝒎𝒆𝒏𝒕(𝑵𝒎) = 𝑭𝒐𝒓𝒄𝒆(𝑵) × 𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝒇𝒓𝒐𝒎 𝑷𝒊𝒗𝒐𝒕(𝒎)

Answer 27

In equilibrium, clockwise moment = anticlockwise moment

Answer 28

Increasing force or distance from the pivot increases the moment of a force

Answer 29

Levers are force magnifiers

Answer 30

Turning a bolt is far easier with a wrench because distance | from pivot is massively increased, and so is the turning effect.

Answer 31

Centre of mass: imaginary point in a body | where total mass of body seems to be acting

Answer 32

Working out the center of mass: Mark three points on the edge of the card Make a hole using a pin on each point Hang it on a cork board and make a line when it is stable Do this for all three points Where all three lines intersect, this is the center of mass

Answer 33

An object will be in stable equilibrium when it returns to its original position given a small displacement

Answer 34

For an object to start rotating it needs to have an unbalanced moment acting on it

Answer 35

A scalar is a quantity that only has a magnitude (so it can only be positive) for example speed.

Answer 36

A vector quantity has a direction as well as a magnitude, for example velocity, which can be negative

Answer 37

Linear momentum: product of mass and velocity | 𝑝 = 𝑚𝑣

Answer 38

when bodies in a system interact, total momentum remains constant provided no external force acts on the system. 𝑚𝐴𝑢𝐴 + 𝑚𝐵𝑢𝐵 = 𝑚𝐴𝑣𝐴 + 𝑚𝐵𝑣B

Answer 39

product of force and time for which it acts | 𝐹𝑡 = 𝑚𝑣 – 𝑚u

Answer 40

amount of work and its measured in Joules (J)

Answer 41

An object may have energy due to its motion or its position

Answer 42

Conservation of energy: energy cannot be created or destroyed, when work is done, energy is changed from one form to another Energy can be stored

Answer 43

Due to motion

Answer 44

From potential to fall

Answer 45

In chemical bonds

Answer 46

Compress/stretch

Answer 47

Atoms rearranged/split

Answer 48

Motion of molecules

Answer 49

Carried by electrons

Answer 50

Carried in light waves

Answer 51

Carried in sound waves

Answer 52

𝐾𝑖𝑛𝑒𝑡𝑖𝑐 𝑒𝑛𝑒𝑟𝑔𝑦 = 1/2 × 𝑀𝑎𝑠𝑠 × 𝑉𝑒𝑙𝑜𝑐𝑖𝑡y² | 𝑲. 𝑬. = 𝟏/𝟐 𝒎v²

Answer 53

𝐺𝑟𝑎𝑣𝑖𝑎𝑡𝑖𝑜𝑛𝑎𝑙 𝑃𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝐸𝑛𝑒𝑟𝑔𝑦 = 𝑀𝑎𝑠𝑠 × 𝐺𝑟𝑎𝑣𝑖𝑡𝑦 × 𝐻𝑒𝑖𝑔ℎ𝑡 | 𝑮.𝑷. 𝑬. = 𝒎𝒈h

Answer 54

A book on a shelf has gravitational potential energy, if it falls of the shelf it will have kinetic energy

Answer 55

Renewable sources are not exhaustible | Non-renewable sources of energy are exhaustible

Answer 56

The sun is the source of energy for all our energy resources except geothermal, nuclear and tidal

Answer 57

In the sun, energy is created through a process called nuclear fusion: hydrogen nuclei are pushed together to form helium.

Answer 58

Efficiency: how much useful work is done with energy supplied

Answer 59

𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 =𝑼𝒔𝒆𝒇𝒖𝒍 𝒆𝒏𝒆𝒓𝒈𝒚 𝒐𝒖𝒕𝒑𝒖𝒕 / 𝑬𝒏𝒆𝒓𝒈𝒚 𝒊𝒏𝒑𝒖𝒕 × 𝟏𝟎𝟎% | 𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 = 𝑼𝒔𝒆𝒇𝒖𝒍 𝒑𝒐𝒘𝒆𝒓 𝒐𝒖𝒕𝒑𝒖𝒕 /𝑷𝒐𝒘𝒆𝒓 𝒊𝒏𝒑𝒖𝒕 × 𝟏𝟎𝟎%

Answer 60

Work is done whenever a force makes something move. The unit for work is the Joule (J). 1 joule of work = force of 1 Newton moves an object by 1 meter

Answer 61

𝑾𝒐𝒓𝒌 𝒅𝒐𝒏𝒆 (𝑱) = 𝑭𝒐𝒓𝒄𝒆 (𝑵) × 𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆 (𝒎) 𝑾 = 𝑭𝑫

Answer 62

Power is the rate of work | The unit for power is Watts (W)

Answer 63

𝑷𝒐𝒘𝒆𝒓 (𝑾) = 𝑾𝒐𝒓𝒌 𝑫𝒐𝒏𝒆 (𝑱) / T𝒊𝒎𝒆 𝑻𝒂𝒌𝒆𝒏 (𝒔)

Answer 64

𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆 (𝑷𝒂) = F𝒐𝒓𝒄𝒆 (𝑵) / 𝑨𝒓𝒆𝒂 (𝒎𝟐) 𝑷 = 𝑭 / 𝑨 Unit: Pascals (Pa) = N/m2

Answer 65

``` 𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆(𝑷𝒂) = 𝑫𝒆𝒏𝒔𝒊𝒕𝒚(𝒌𝒈/𝒎𝟑) × 𝑮𝒓𝒂𝒗𝒊𝒕𝒚(𝒎/𝒔𝟐) × 𝑯𝒆𝒊𝒈𝒉𝒕(𝒎) 𝑷 = 𝒉𝝆𝒈 ```

Answer 66

At a depth of 10m in water, the pressure is always 100,000 Pa (1bar) and is constant for each further 10m.

Answer 67

1 atm = 101.325 X 103 Pa = 101 KPa

Answer 68

A manometer measures the pressure difference. The height difference shows the excess pressure in addition to the atmospheric pressure.

Answer 69

Tube with vacuum at the topand mercury filling the rest. Pressure of the air pushesdown on reservoir, forcingmercury up the tube. Measure height of mercury ~760 mm of mercury is 1 atm

Answer 70

``` Fixed shape and volume Strong forces of attraction between particles Fixed pattern (lattice) Atoms vibrate but can’t change position: fixed volume and shape ```

Answer 71

Fixed volume but changes shape depending on its container Weaker attractive forces than solids No fixed pattern, liquids take shape of their container Particles slide past each other

Answer 72

No fixed shape or volume, gases fill up their containers Almost no intermolecular forces Particles far apart, and move quickly Collide with each other and bounce in all directions

Answer 73

The pressure gases exert on a container is due to the particles colliding on the container walls. If the volume is constant, then increasing the temperature will increase the pressure.

Answer 74

Gas molecules move at a random motion This is because of repeated collisions with other gas molecules Small molecules move much faster and have higher energy than larger molecules The small particles can help move the larger particles Brownian motion can be seen visually in smoke

Answer 75

It is the escape of the more energetic particles and occurs | constantly on the surface of liquids

Answer 76

If more energetic particles escape, liquid contains few high energy particles and more low energy particles so average temperature decreases.

Answer 77

Evaporation can be accelerated by: o Increasing temperature: more particles have energy to escape o Increasing surface area: more molecules are close to the surface o Reduce humidity level in air: if the air is less humid, fewer particles are condensing. o Blow air across the surface: removes molecules before they can return to the liquid

Answer 78

Solids, liquids and gasses expand when they are heated as atoms vibrate more and this causes them to become further apart, taking up a greater volume. Due to differences in molecular structure of the different states of matter, expansion is greatest in gases, less so in liquids and lowest in solids

Answer 79

Overhead cables have to be slack so that on cold days, when they contract, they don’t snap or detach. Gaps have to be left in bridge to allow for expansion Bimetal thermostat: when temperature gets too high, bimetal strip bends, to make contacts separate until temperature falls enough, then metal strip will become straight again and contacts touch, to maintain a steady temperature For a fixed mass of gas at constant pressure, the volume is directly proportional to the Kelvin temperature

Answer 80

For a fixed mass of gas at constant pressure, the volume is directly proportional to the Kelvin temperature

Answer 81

A physical property that varies with temperature may be used for measurement of temperature

Answer 82

As temperature rises or falls, the liquid (mercury or alcohol) expands or contracts. Amount of expansion can be matched to temperature on a scale.

Answer 83

The probe contains a thermistor The thermistor is a material that becomes a better electrical conductor when the temperature rises (semi-conductor) So when temperature increases, a higher current flows from a battery, causing a higher reading on the meter

Answer 84

The probe contains 2 different metals joined metals to form 2 junctions. The temperature difference causes a tiny voltage which makes a current flow. A greater temperature difference gives a greater current. Thermocouple thermometers are used for high temperatures which change rapidly and have a large range (-200C° to 1100°C)

Answer 85

Fixed points are definite temperatures at which something happens and are used to calibrate a thermometer. For example, melting and boiling point of water

Answer 86

Place thermometer in melting ice, this is 0 °C. | Place thermometer in boiling water, this is 100 °C

Answer 87

Sensitivity: change in length or volume per degree

Answer 88

To increase sensitivity: Thinner capillary Less dense liquid Bigger bulb

Answer 89

Range: change the upper and lower fixed points

Answer 90

Linearity: change the distance between intervals Responsiveness: how long it takes for the thermometer to react to a change in temperature

Answer 91

This is when a solid turns into a liquid. Temperature increases thus kinetic energy in solid increases and particles vibrate more rapidly but there is no increase in temperature of the substance when melting because thermal energy supplied is instead being used to break bonds between particles of the solid thus making it into a liquid.

Answer 92

Boiling point is the temperature at which a substance boils

Answer 93

This is when a liquid turns into a gas Temperature increases thus kinetic energy in liquid increases and particles vibrate more rapidly but there is no increase in temperature of the substance when boiling because thermal energy supplied is instead being used to break bonds between particles of the liquid thus making it into a gas.

Answer 94

Melting point is the temperature at which a substance melts

Answer 95

Boiling occurs at a fixed temperature and throughout the liquid Evaporation occurs at any temperature and only on the surface

Answer 96

The latent heat of fusion is the amount of energy needed to melt 1Kg of a substance.

Answer 97

The latent heat of vaporization is the amount of energy needed to boil 1Kg of a substance

Answer 98

𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝐿𝑎𝑡𝑒𝑛𝑡 𝐻𝑒𝑎𝑡 𝑜𝑓 𝐹𝑢𝑠𝑖𝑜𝑛 = 𝐸𝑛𝑒𝑟𝑔𝑦 𝑇𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑 / 𝑀𝑎𝑠𝑠 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝐿𝑎𝑡𝑒𝑛𝑡 𝐻𝑒𝑎𝑡 𝑜𝑓 𝑉𝑎𝑝𝑜𝑟𝑖𝑧𝑎𝑡𝑖𝑜𝑛 = 𝐸𝑛𝑒𝑟𝑔𝑦 𝑇𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑 / 𝑀𝑎𝑠𝑠

Answer 99

Condensation is when a gas turns back into a liquid.

Answer 100

When a gas is cooled, the particles lose energy. They move more and more slowly. When they bump into each other, they do not have enough energy to bounce away again so they stay close together, and a liquid forms

Answer 101

When a liquid cools, the particles slow down even more. Eventually they stop moving except for vibrations and a solid forms.

Answer 102

Good conductors are used whenever heat is required to travel quickly through something Bad conductors (insulators) are used to reduce the amount of heat lost to the surroundings

Answer 103

Conduction is the flow of heat through matter from places of higher temperature to places of lower temperature without movement of the matter as a whole

Answer 104

In non-metals - when heat is supplied to something, its atoms vibrate faster and pass on their vibrations to the adjacent atoms.

Answer 105

In metals – conduction happens in the previous way and in a quicker way –electrons are free to move, they travel randomly in the metal and collide with atoms and pass on the vibrations.

Answer 106

Convection is the flow of heat through a fluid from places of higher temperature in places of lower temperature by movement of the fluid itself.

Answer 107

As a fluid (liquid or gas) warms up, the particles which are warmer become less dense and rise. They then cool and fall back to the heat source, creating a cycle called convection current. As particles circulate they transfer energy to other particles. If a cooling object is above a fluid it will create a convection current

Answer 108

Radiation is the flow of heat from one place to another by means of electromagnetic waves

Answer 109

Thermal radiation is mainly infra-red waves, but very hot objects also give out light waves. Infra-red radiation is part of the electromagnetic spectrum.

Answer 110

A reflector reflects thermal radiation, | therefore is a bad absorber.

Answer 111

An emitter will cool down quickly, an absorber will heat up more quickly and a reflector will not heat up quickly

Answer 112

Solar panel: the sun’s thermal radiation is absorbed by a matt black surface and warms up the pipes containing water

Answer 113

Refrigerator: the freezer compartment is located at the top of the refrigerator. It cools down the air which then sinks. Any warm air rises to the top and then is cooled. This creates a convection current which maintains a cold temperature

Answer 114

Metals used in cooking pans because they conduct heat well

Answer 115

Metal spoon in a hot drink will warm up because it conducts heat Convection currents create sea breezes. During the day the land is warmer and acts as heat source. During the night the sea acts as the heat source. A black saucepan cools better than a white one, white houses stay cooler than dark ones

Answer 116

Waves transfer energy without transferring matter

Answer 117

Frequency: the number of waves passing any point per second | measured in hertz (Hz)

Answer 118

Period: time taken for one oscillation in seconds

Answer 119

Wavefront: the peak of a transverse wave or the compression of a longitudinal wave

Answer 120

Speed: how fast the wave travels measured in m/s

Answer 121

Wavelength: distance between a point on one wave to the | equivalent point on the next wave in meters

Answer 122

Amplitude: maximum distance a wave moves from its rest | position when a wave passes

Answer 123

Travelling waves in which oscillation is perpendicular to direction of travel Has crests and troughs For example, light, water waves and vibrating string

Answer 124

Travelling waves in which oscillation is parallel to direction of travel. Has compressions and rarefactions For example, sound waves

Answer 125

Speed and wave length is reduced but frequency stays the same and the wave changes direction Waves slow down when they pass from a less to a more dense material and vice versa

Answer 126

When wave is slowed down, it is refracted towards normal (i > r) When wave is sped up, it is refracted away from normal (i < r)

Answer 127

Deep water is denser than shallow water

Answer 128

``` When water wave travels from deep to shallow; speed decreases, wavelength decreases and frequency remains constant ```

Answer 129

``` When water waves travel from shallow to deep; speed increases wavelength increases and frequency remains constant ```

Answer 130

Waves bounce away from surface at same angle they strike it Angle of incidence = angle of reflection Speed, wavelength and frequency are unchanged by reflection

Answer 131

``` Waves bend round the sides of an obstacle, or spread out as they pass through a gap. Wider gaps produce less diffraction. When the gap size is equal to the wavelength, maximum diffraction occurs ```

Answer 132

Plane (flat) mirrors produce a reflection

Answer 133

Rays from an object reflect off the mirror into our eyes, | but we see them behind the mirror

Answer 134

Image is the same size as the object Image is the same distance from the mirror as the object A line joining equivalent points of the image and object meet the mirror at a right angle Image is virtual: no rays actually pass through the image and the image cannot be formed on a screen

Answer 135

Angle of incidence = angle of reflection The incident ray, reflected ray and normal are always on the same plane (side of mirror)

Answer 136

Refraction is the bending when light travels from one medium to another

Answer 137

Angle at which refracted ray is parallel to the surface of material. If angle of incidence is greater than the critical angle there is no refracted ray, there is total internal reflection. If angle of incidence is less than the critical angle the incidence ray will split into a refracted ray and a weaker reflected ray

Answer 138

Light put in at one end is totally internally reflected until it comes out the other end. Used in communications: signals are coded and sent along the fiber as pulses of laser light Used in medicine: an endoscope, an instrument used by surgeons to look inside the body; contains a long bundle of optic fibers.

Answer 139

Principal focus: the point where rays parallel to the principal axis converge with a converging lens.

Answer 140

Focal length: distance from principle focus and the optical center

Answer 141

Principal axis: line that goes through optical center, and the 2 foci

Answer 142

Optical center: the center of the lens

Answer 143

Real: image can be caught on a screen

Answer 144

Virtual: image cannot be caught on a screen

Answer 145

Real: when object is further away from the optical centre than F’ is Virtual: When the object is closer to the optical centre than F’ is

Answer 146

``` When light is refracted by a prism, the incidence ray is not parallel to the emergent ray, since the prism’s sides are not parallel. ```

Answer 147

If a beam of white light is passed through a prism it is dispersed into a spectrum. White light is a mixture of colors, and the prism refracts each color by a different amount – red is deviated least & violet most

Answer 148

Travel at the speed of light: 3 × (10 to the power of 8) m/s Don’t need a medium to travel through (travel through a vacuum) Can transfer energy Are produced by particles oscillating or losing energy in some way Are transverse waves

Answer 149

Radio waves: radio and television communications

Answer 150

Microwaves: satellite television and telephones | Safety issue: cause internal heating of body tissues

Answer 151

Infrared: electrical appliances (radiant heaters and grills), remote controllers for televisions and intruder alarms

Answer 152

X-rays: medicine (x-ray photography and killing cancer cells) and security o Safety issue: is a mutagen, it cause cancer (mutations)

Answer 153

Monochromatic: light of a single wavelength and color (used in lasers)

Answer 154

Sound waves come from a vibrating source e.g. loudspeaker As the loudspeaker cone vibrates, it moves forwards and backwards, which squashes and stretches the air in front As a result, a series of compressions (squashes) and rarefactions (stretches) travel out through the air, these are sound waves.

Answer 155

Sound waves are longitudinal: they have compressions and rarefactions and oscillate backwards and forwards. Humans can hear frequencies between 20 and 20 000Hz. Sound waves need a medium to travel through.

Answer 156

Ultrasound Waves: high frequency sound waves, medically used to look at structures and organs inside the human body, i.e. to form an image of a fetus in a pregnancy

Answer 157

Compression: high pressure section of the wave Rarefaction: low pressure section of the wave

Answer 158

The higher the frequency, the higher the pitch. | The higher the amplitude, the louder the sound.

Answer 159

Medium State speed Concrete Solid 5000 m/s Pure Water Liquid 1400 m/s Air Gas 330 m/s

Answer 160

Has a magnetic field around it Has 2 opposite poles (North and South) which exert forces on other magnets. Like poles repel and unlike poles attract. Will attract magnetic materials by inducing (permanent or temporary) magnetism in them. Will exert little or no force on a non-magnetic material The direction of an electric field at a point is the direction of the force on a positive charge at that point

Answer 161

Magnets attract materials by inducing magnetism in them; the material becomes a magnet as well. The side of the material facing the magnet will become the opposite pole as the magnet.

Answer 162

A piece of steel becomes permanently magnetized when placed near a magnet, but its magnetism is usually weak. It can be magnetized more strongly by stroking it with one end of a magnet Most effective method: place it in a solenoid and pass a large, direct current (d.c.) through the coil.

Answer 163

If a magnet is hammered, its atomic magnets are thrown out of line and it becomes demagnetized. Heating a magnet to a high temperature also demagnetize it. Most efficient method: place magnet inside a solenoid connected to an alternating current (a.c.) supply

Answer 164

``` Design: Hard magnetic material Use: For applications where magnetism is needed over long periods – fridge doors ```

Answer 165

``` Design: Uses a solenoid to create magnetic field Use: For applications where magnetic field needs to be turned on & off - scrap metal moving ```

Answer 166

You can detect an electrostatic charge using a leaf electroscope. If a charged object is placed near the cap, charges are induced. The metal cap gets one type of charge (positive or negative) and the metal stem and gold leaf get the other type of charge so they repel each other

Answer 167

There are 2 types of charges: positive and negative. | Unlike charges attract and like charges repel.

Answer 168

Electric field: region in which electric charge experiences a force

Answer 169

Conductors: materials that let electrons pass through them Metals are the best electrical conductors as they have free electrons.

Answer 170

Insulators: materials that hardly conduct at all. o Their electrons are tightly held to atoms and hardly move, but they can be transferred by rubbing

Answer 171

The SI unit of charge is the Coulomb (C).

Answer 172

Parallel plates Point charge +ve and -ve +ve and +ve

Answer 173

A charge that “appears” on an uncharged object because of a charged object nearby For example if a positively charged rod is brought near a small piece of aluminum foil, electrons in foil are pulled towards rod, which leaves the bottom of the foil with a net positive charge. The attraction is stronger than repulsion because the attracting charges are closer than the repelling ones

Answer 174

Current: a flow of charge, the SI unit is the Ampere (A). An ammeter measures the current in a circuit and is connected in series Current is a rate of flow of charge. 𝐶ℎ𝑎𝑟𝑔𝑒 (𝐶) = 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴) × 𝑇𝑖𝑚𝑒 (𝑠) 𝑄 = 𝐼𝑡 Current follows path of least resistance

Answer 175

The conventional current is the opposite of what actually | happens.

Answer 176

The maximum voltage a cell can produce is called the electromotive force (EMF), measured in volts. When a current is being supplied, the voltage is lower because of the energy wastage inside the cell. A cell produces its maximum PD when not in a circuit and not supplying current.

Answer 177

Potential difference, or PD for short, is also known as voltage.

Answer 178

Voltage is the amount of energy the cell gives the electrons it pushes out. Voltage is measured in volts (V) and is measured by a voltmeter (connected in parallel). If a cell has 1 Volt, it delivers 1 Joule of energy to each coulomb of charge (J/C).

Answer 179

𝑉𝑜𝑙𝑡𝑎𝑔𝑒 = 𝐸𝑛𝑒𝑟𝑔𝑦 / 𝐶ℎ𝑎𝑟𝑔𝑒 | 𝑉 =𝐸 / C

Answer 180

``` 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 / 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 = (Ω) = 𝑉 / 𝐼 ```

Answer 181

Factors affecting resistance: Length Cross-sectional area Material Better conductor = less resistance Temperature For metal conductors higher temperature = more resistance For semi-metal conductors higher temperature = less resistance

Answer 182

Ohm’s law states that voltage across a resistor is directly proportional to the current through it. This is only true if the temperature of the resistor remains constant.

Answer 183

1 Watt is 1J/s

Answer 184

𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑝𝑜𝑤𝑒𝑟 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉) × 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴)

Answer 185

𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉) × 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴) × 𝑡𝑖𝑚𝑒 (𝑠)

Answer 186

Supplies electrical energy. Larger terminal (left) is positive (+).

Answer 187

``` Supplies electrical energy. A battery is more than one cell. Larger terminal (left) is positive (+) ```

Answer 188

Flows in one direction

Answer 189

Flows in both direction

Answer 190

Allows current only to flow when the switch is closed

Answer 191

Restrict the flow of | current.

Answer 192

Used to control current (by varying the resistance)

Answer 193

Resistor whose resistance varies with temperature

Answer 194

Resistor whose resistance varies with light intensity

Answer 195

Transducer which converts electrical energy to light

Answer 196

Measure current

Answer 197

Measure voltage

Answer 198

Type of sensitive ammeter; instrument for detecting electric current.

Answer 199

``` Two coils of wire linked by an iron core. Transformers are used to increase and decrease AC voltages. ```

Answer 200

Transducer which converts electrical energy to sound

Answer 201

``` A safety device which will 'blow' (melt) if current flowing through it exceeds specified value, breaking circuit ```

Answer 202

An electrically operated switch, e.g. a 9V battery circuit connected to the coil can switch a 230V AC mains circuit (the electromagnet is used to pull away the contacts and vice versa)

Answer 203

The current at any point in a series circuit is the same The current splits at each branch in a parallel circuit so the total current is always greater than the current in one branch

Answer 204

The combined resistance of 2 resistors in parallel is less than that of either resistor by itself

Answer 205

Advantages of putting lamps in parallel are: o If one lamp breaks, the other still works o Each lamp gets maximum PD

Answer 206

In series: PD across the supply = PD across all the components combined In parallel: Current across the source = sum of currents in the separate branches

Answer 207

A potential divider divides the voltage into smaller parts.

Answer 208

Thermistor: input sensor and a transducer. It is a temperature-dependent resistor. At higher temperature there is less resistance.

Answer 209

Light dependent resistor (LDR): input sensor and a transducer. When light intensity increases, resistance decreases.

Answer 210

A switch operated by an electromagnet

Answer 211

Normal Closed Relay: When coil not energised, switch is closed, completing circuit Normally Open Relay: When coil is energised, switch is closed, completing circuit

Answer 212

A device that has an extremely high resistance in one direction and a low resistance in the other, therefore it effectively only allows current to flow in one direction Forward bias is when the diode is pointing in the direction of the conventional current and reverse bias is the opposite It can be used in a rectifier; turns AC current into DC current.

Answer 213

Analogue uses a whole range of continuous variations to transmit a signal.

Answer 214

Digital signals use only 2 states, on and off.

Answer 215

Logic gates are processors that are circuits containing transistors and other components.

Answer 216

Damaged insulation: contact with the wire (live wire especially) due to gap in the insulation causes electric shock which can cause serious injury or shock.

Answer 217

Overheating of cables: when long extension leads are coiled up, they may overheat. The current warms the wire, but the heat has less area to escape from a tight bundle. This might cause a fire.

Answer 218

Damp conditions: water can conduct a current, so if electrical equipment is wet someone might get electrocuted

Answer 219

A fuse protects a circuit. Thin piece of wire which overheats and melts if current is too high. It is placed on the live wire before the switch. This prevents overheating and catching fire. A fuse will have a specific current value (e.g. 13A) so when choosing a suitable fuse you must use the one above minimum value but less than maxiumum value

Answer 220

An automatic switch which if current rises over a specified value, the electromagnet pulls the contacts apart, breaking the circuit. The reset button is to rest everything. It works like a fuse but is better because it can be reset.

Answer 221

Many electrical appliances, have metal cases, the earth wire creates a safe route for current to flow through, if live wire touches casing Earth terminal connected to metal casing, so the current goes through earth wire instead of causing an electric shock. A strong current surges through earth wire because it has very low resistance This breaks the fuse and disconnects the appliance.

Answer 222

If a wire is passed across a magnetic field, a small EMF is induced If the wire forms part of a complete circuit, the EMF makes a current flow and this can be detected using a galvanometer. The EMF induced in a conductor is proportional to the rate at which the magnetic field lines are cut by the conductor.

Answer 223

``` The induced EMF can be increased by: moving the wire faster using a stronger magnet Increasing length of wire in magnetic field, e.g. looping the wire through the field several times. ```

Answer 224

The current and EMF direction can be reversed by: moving the wire in the opposite direction o turning the magnet round so that the field direction is reversed

Answer 225

Fleming’s right-hand rule

Answer 226

moving the magnet faster using a stronger magnet increasing the number of turns in the coil

Answer 227

If the magnet is pulled away, the direction of the induced EMF (and current) is reversed

Answer 228

``` Using South pole instead of North pole reverses direction of induced EMF (and current) ```

Answer 229

there is no EMF

Answer 230

An induced current always flows in a direction such that it | opposes the change which produced it

Answer 231

When a magnet is moved towards a coil the pole of the coil and magnet next to each other are the same

Answer 232

When the magnet is moved away the poles are opposite (opposite poles attract)

Answer 233

The pole-type (north or south) is controlled by the direction in which the current is induced

Answer 234

The direction of the current is given by the right-hand grip rule: The fingers point in the conventional current direction and the thumb gives the North Pole.

Answer 235

The oil is made of insulated copper wire and is rotated by turning the shaft; the slip rings are fixed to the coil and rotate with it.

Answer 236

The brushes are 2 contacts which rub against the slip rings and keep the coil connected to the outside part of the circuit, usually made of carbon.

Answer 237

When the coil is rotated, it cuts magnetic field lines, so an EMF is generated, which makes a current flow.

Answer 238

The current is maximum when the coil is horizontal since field lines are being cut at the fastest rate and 0 when the coil is vertical, since it is cutting NO field lines.

Answer 239

increasing the number of turns on the coil increasing the area of the coil using a stronger magnet rotating the coil faster

Answer 240

AC currents can be increased or decreased by using a transformer

Answer 241

Consists of a primary coil, a secondary coil and an iron core. The iron core gets magnetized by the incoming current and this magnetism then creates a current in the leaving wire. The power is the same on both sides (assume= 100% efficiency)

Answer 242

𝑶𝒖𝒕𝒑𝒖𝒕 𝒗𝒐𝒍𝒕𝒂𝒈𝒆 / 𝑰𝒏𝒑𝒖𝒕 𝒗𝒐𝒍𝒕𝒂𝒈𝒆 = 𝑻𝒖𝒓𝒏𝒔 𝒐𝒏 𝒐𝒖𝒕𝒑𝒖𝒕 𝒄𝒐𝒊𝒍 / 𝑻𝒖𝒓𝒏𝒔 𝒐𝒏 𝒊𝒏𝒑𝒖𝒕 𝒄𝒐𝒊l

Answer 243

A step-up transformer increases the voltage and a step-down | transformer decreases it.

Answer 244

Transformers used to make high voltage AC currents.

Answer 245

Since transmission cables are many kilometres long they have a lot of resistance, so a transformer is used to increase the voltage and decrease the current to decease power lost.

Answer 246

less power lost thinner, light, and cheaper cables can be used since current is reduced

Answer 247

Magnetic effect of current is used in a relay and a circuit breaker

Answer 248

If a current carrying conductor is in a magnetic field, it warps the field lines. The field lines from the magnet want to straighten out naturally. This causes a catapult like action on the wire creating a force.

Answer 249

If you reverse current, you will reverse direction of force

Answer 250

If you reverse direction of field, you will reverse direction of force

Answer 251

The direction of the force, current or magnetic field is given by Fleming’s left-hand rule

Answer 252

A DC motor runs on a direct current.

Answer 253

When a current-carrying coil is in a magnetic field, it experiences a turning effect

Answer 254

The coil is made of insulated copper wire and is free to rotate between the poles of the magnet. The commutator (split-ring) is fixed to the coil and rotates with it

Answer 255

``` Increasing the current Using a stronger magnet Increasing length of coils by: Increasing number of coils increasing area of the coil ```

Answer 256

- reversing the battery | - reversing the poles

Answer 257

Background radiation: small amount of radiation around us all time because of radioactive materials in the environment. It mainly comes from natural sources such as soil, rocks, air, building materials, food and drink – and even space.

Answer 258

The ‘window’ is thin enough for alpha particles to pass through. If an alpha particle enters the tube, it ionizes the gas inside. This sets off a high-voltage spark across the gas and a pulse of current in the circuit. A beta particle or gamma radiation has the same effect. It can be connected to a rate meter (tells the counts per seconds) or a scaler (tells total number of particles or bursts of gamma radiation)

Answer 259

Radioactive decay: A radioisotope (unstable arrangement of neutrons and protons) is altered to make a more stable arrangement. The parent nucleus becomes a daughter nucleus and a particle (decay products).

Answer 260

An element with a proton number 2 lower and nucleon number 4 lower, and an alpha particle is made (2p + 2n) e.g. Radium-226 nucleus → Radon-222 + helium-4 nucleus

Answer 261

Gamma emission by itself causes no change in mass number or atomic number; they just emit energy Some isotopes do not change in mass or atomic number however they emit energy as their particles rearrange themselves to become more stable

Answer 262

Half-life of a radioisotope: is the time taken for half the nuclei present in any given sample to decay. Some nuclei are more stable than others.

Answer 263

Radioactive material is stored in a lead container and locked away Picked up with tongs, not bare hands Kept away from the body and not pointed at people Left out of its container for as short a time as possible

Answer 264

Atoms consist of: Nucleus: central part of atom made of protons (positively charged) and neutrons. These two types of particles are called nucleons. They are bound together by the strong nuclear force. Electrons: almost mass-less particles which orbit nucleus in shells

Answer 265

Thin gold foil is bombarded with alpha particles, which are positively charged. Most passed straight through, but few were repelled so strongly that they were bounced back or deflected at large angles. Rutherford concluded that the atom must be largely empty space, with its positive charge and most of its mass concentrated in a tiny nucleus.

Answer 266

``` The nucleus is composed of protons and neutrons. Proton number: number of protons in an atom Nucleon number: the number of nucleons (protons + neutrons) in an atom ```

Answer 267

Isotope: atoms of the same element that have different numbers of neutrons e.g. Carbon 12 and Carbon 14. There are non-radioactive isotopes and radio-isotopes. Radio isotopes are unstable atoms, which break down giving radiation Medical use: cancer treatment (radiotherapy) – rays kill cancer cells using cobalt-60 Industrial use: to check for leaks – radioisotopes (tracers) added to oil/gas. At leaks radiation is detected using a Geiger counter. Archaeological use: carbon 14 – used for carbon dating

Answer 268

(thermal) energy required to heat unit mass / 1 kg / 1 g | by unit temperature / 1 °C / 1 K

Answer 269

density = mass/volume

Answer 270

Energy divided by mass multiplied by temperature increase/decrease

Answer 271

Heat required to change the state of (melt) unit mass (1 kg or 1 g ) of solid with no change of temperature (Allow specific example e.g. ice to water)

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