Contents Page Weight 4 – 5 Work Done 6 – 7 Gravitational Potential Energy 8 – 9 Kinetic Energy 10 – 11 Conservation of Energy – Falling Objects 12 – 13 Efficiency 14 – 15 Electric Charge 16 – 17 Electrical Current 18 – 19 Charges in Electric Fields 20 Series Circuits 21 – 22 Parallel Circuits 23 – 24 Mixed Circuits 25 Ohm’s Law 26 – 27 Variable Resistors 28 Solar (Photovoltaic) Cells 29 Capacitors 30 LEDs 31 Thermistors and LDRs 32 – 33 Resistors in Series 34 Resistors in Parallel 35 Resistors in Mixed Circuits 36 – 38 Voltage Dividers 39 – 41 Switching Circuits 42 – 47 Electrical Power 48 – 50 Power, Current & Voltage 51 – 52 Fuses 53 Power & Resistance 54 – 57 Specific Heat Capacity 58 – 59 Heat Transfer 60 Pressure 61 – 62 Gas Laws 63 – 67
Q is the charge flowing through a component (C) I is the current flowing through a component (A) t is the time (s) What is an electrical current? Copy and complete this table: Charge / C Current / A Time / s (a) 0.5 30 (b) 0.14 25 (c) 4.2 15 (d) 3200 1280 (e) 1.6 x 10-3 3.2 x 10-4 (f) 270 0.3 A current of 6.5 A flows through a hairdryer for 5 minutes. What is the charge that flows through the hairdryer during this time? When playing a game, an Xbox 360 has 1368 coulombs of charge flo wing through it an hour. What is the current flowing through the console? An electric kettle has 9.5 A of current flowing through it as it water. How long does it take the kettle to boil if 1995 C of charge flows through it before it switches off? What is the difference between alternating and direct current?
T is the temperature of a fixed mass of gas (K) Explain, using the kinetic theory of particles, what happens to the particles in a liquid when it melts and becomes a gas. Explain, using kinetic theory, how the air in a bicycle tyre creates pressure on the inside surface of the tyre. Why does the Kelvin temperature scale start at -273 °C? Convert these temperatures from degrees Celsius to Kelvin. 0 °C 20 °C -273 °C 100 °C A conical flask is sealed with air inside, and is placed in a heat bath. The temperature of the gas increases from 20 °C to 70°C. After every 10 °C temperature increase, the pressure of the gas is measured using a Bourdon gauge. The results are shown. Temperature / °C Pressure / x 105 Pa 20 1.01 30 1.04 40 1.08 50 1.11 60 1.15 70 1.18
In an experiment, an open capillary tube with a mercury thread is placed in to a heat bath. As the temperature of the gas increases, the mercury thread moves up the capillary tube. The pressure of the gas remains constant because the capillary tube is open. The temperature of the gas is measured with a thermometer and the volume of the gas is measured a scale next to the open capillary tube. The results of the experiment are shown. Temperature / °C Volume / cm3 20 1.50 25 1.88 30 2.25 35 2.63 40 3.00 45 3.38 Using the data, draw a line graph of volume against temperature (in degrees Celsius). Make sure that your temperature axis goes from -300 °C to 45 °C. Using the data, draw a line graph of volume against temperature (in Kelvin). What do these two graphs tell you about the relationship between the volume and temperature of a fixed mass of gas? Explain this relationship in terms of the kinetic theory of particles. The volume of a fixed mass of gas is 30.0 cm3 at 30 °C. The temperature of the gas is increased to 60 °C without changing the pressure. A student makes this statement: ‘As the temperature of the gas has doubled, the volume of the gas will also double. Therefore, the volume of the gas at 60 °C will be 60.0 cm3.’ Explain why this statement is incorrect. Calculate what the volume of the gas actually be at 60 °C. Air is trapped in a glass capillary tube by a bead of mercury. The volume of air is found to be 0.15 cm3 at a temperature of 27 °C.
Assuming that the pressure of the air remains constant, what is the volume of the air at a temperature of 87 °C? A fixed mass of gas is trapped in to a syringe. The gas has a pressure of 1.63 x 105 Pa when it has a volume of 3.0 cm3 and a temperature of 22 °C. The gas is then heated it has a uniform temperature of 57 °C. What will be the pressure of the gas if the volume of the gas is increased to 5.0 cm3? Answers Weight (p4 – 5) Mass is a measure of how much of an object is there. It is measured in kg. Weight is a downward force caused by gravity. It is measured in N. (a) 30 N 2.25 N 30 kg 30 kg 8 N kg-1 26 N kg-1 (a) 30 N 1 N 650 N 12 000 N The weight of the space shuttle decreases. This is because: There is less mass due to fuel being used up. The shuttle is getting further away from the surface of the Earth. 85 kg (a) 372 N 2418 N 372 N 0 N 75 kg Saturn (a) 13 N kg-1 Person pushes down on scales. Scales push back up on person. Work Done (p6 – 7)
14.1 m/s (a) 0.69 J 5.48 m s-1 5.48 m s-1 (a) 224 m s-1 Air resistance is slowing the skydiver down. (a) 1.6 J 3.2 m (a) 810 000 J 600 000 J 210 000 J 9.2 m s-1 1.96 m s-1 21.4 m s-1 Efficiency (p14 – 15) (a) Electrical Light Electrical Heat Gravitational Potential Kinetic Light Electrical Electrical Sound (a) Chemical Heat Kinetic Electrical Water is stored in a high reservoir behind a dam. The water is released through the dam in to a low level reservoir. The gravitational potential energy of the is turned in to kinetic energy, which turns turbines which generate electricity. Heat energy is lost to the surroundings in many places (boiler, etc.) (a) 25 kJ 16 250 J Missing energy is lost as heat and sound energy to the surroundings. (a) 60 % 5 % 2795 J 12 160 000 J 108 000 J 4 875 000 J 35 % 486 J (a) Electrical Sound 5488 J 6 240 000J 792 000 J Electrical Charge (p16 – 17) The image of the document is projected on to a positively charged copying plate. Where light is incident on the plate, charge leaks away. The negatively charged toner particles are attracted to the remaining positive areas. Paper is placed over the copying plate. The toner is transferred to the paper and sticks after heating. ‘Fluffing up’ a static duster causes it to become charged. This attracts charged particles to the duster. (a) The droplets of paint have the same charge so spread out more when sprayed. This keeps the coat of paint even.
The car body has an opposite charge so paint drops that would miss are attracted to it. (a) When you unroll cling film, negative charges (electrons) from one layer get pulled across to the other. This creates patches of positive and negative charges. The plastic bowl is an electrical insulator. The negative charges can flow through the conducting bowl and away from the cling film. (a) Air and dust particles enter the precipitator through a negatively charged metal grid. The dust particles can be charged but the air particles can’t. Dust particles are then attracted to positively charged plates. This only leaves air particles leaving the precipitator. Fossil fuel power stations can clean their emissions so less smoke is released in to the atmosphere. Electrical Current (p18 – 19) Electrical current is a flow of electrons. It is the amount of charge that flows through a component in one second. (a) 15 C 3.5 C 0.28 A 2.5 A 5 s 900 s 1950 C 0.38 A 210 s Alternating current constantly changes direction. Direct current only flows in one direction – from negative to positive. (a) Alternating current Direct current (a) (i) 6V (ii) 50 Hz (i) 3 V (ii) 100 Hz Charges in Electric Fields (p20) (a) Y (b) Z (c) X Series Circuits (p21 – 22) (a) I1 = 0.4 A, I2 = 0.4 A I1 = 6.5 A, I2 = 6.5 A
As temperature increases, current increases. Any value greater than 5700 Ω. As brightness of increases, the resistance decreases. As brightness of light increases, the current increases. Any resistance greater than 3.3 kΩ. Resistors in Series (p34) As more resistors are connected in series, the total resistance increases. (a) 245 Ω 950 Ω 830 Ω 625 Ω (a) 550 Ω 6390 Ω Resistors in Parallel (p35) As more resistors are connected in parallel, the total resistance decreases. (a) 20 Ω 30 Ω 600 Ω 150 Ω (a) 40 Ω 300 Ω Resistors in Mixed Circuits (p36 – 38) (a) 44 Ω 30 Ω 75 Ω 600 Ω 45 Ω (a) 108 Ω 12 Ω 54 Ω 24 Ω (b) Is the lowest resistance 400 Ω Voltage Dividers (p39 – 41) As its resistance increases, voltage across a resistor also increases.
As resistance increases, electrons will lose more energy as they pass through the resistor. Therefore, the voltage across the resistor will increase. (a) 125 Ω 225 Ω 1.2 kΩ (a) 250 Ω 300 Ω 40 Ω (a) 3 V 3V 0.5 V (a) 3.8 V 1.0 V 0.6 V (a) V1 = 6 V, V2 = 6 V V1 = 4 V, V2 = 10 V V1 = 7 V, V2 = 3 V V1 = 16 V, V2 = 6 V V1 = 4.5 V, V2 = 13.5 V V1 = 5.5 V, V2 = 3 V Switching Circuits (p42 – 47) (a) 0V 15 V 15 V 0V (a) 4V 8 V 0 V 12 V (a) 700 Ω 3.5 V 2.5 V 3 V 100 °C (a) 6 V 2.5 V 0.016 A (a) (NPN) Transistor As the temperature increases, the resistance of the thermistor decreases. The voltage across the thermistor decreases and the voltage across R1 increases. When this voltage reaches 0.7 V, the transistor switches on and the LED lights. Swap the positions of the thermistor and R1. (a) MOSFET As brightness of light decreases, the resistance of the LDR increases. The voltage across the LDR increases. When this reaches a high enough voltage, the MOSFET switches on and the lamp lights. The brightness at which the lamp turns on can be altered. (a) 13.3 V 1900 Ω 150 Ω This circuit could turn on a fan when a computer overheats. As the temperature increases, the resistance of the thermistor decreases. The voltage across the thermistor decreases and the voltage across R1 increases. When this voltage reaches 0.7 V, the transistor switches on and the LED lights. Electrical Power (p48 – 50) The light bulb uses up 60 J of electrical energy every second.
(a) 80 W 85 W 45 000 J 1 305 000 J 250 s 140 s 90 W 62 640 000 J 600 s (a) 748 800 J 28 800 J Standby = 138 240 J Full Power = 140 400 J Full for 45 minutes uses up more energy. (a) 306 000 J 2.5 hours 158 400 – 25 200 = 133 200 J 1300 W Power, Current & Voltage (p51 – 52) (a) 1.35 W 18 W 30 A 5 A 50 V 40 V 759 W 3.5 A 12 V 0.52 A 110 V (approximately) Fuses (p53) The fuse protects the flex of an appliance from damage due to a high current. If a occurs, the current can get much higher than is safe (up to 13 A). This can cause dangerous overheating of the flex. The fuse will blow as the current is greater than 3 A. The current is above 3A when the vacuum is turned on although the current drops below 3A when it is in normal operation. More current is required to start the motor. 3 A fuse (I = 0.87 A) 10 A fuse ( I = 5.2 A) 13 A fuse (I = 10.9 A) 5A fuse (I = 4.35 A) Power & Resistance (p54 – 57) P = I V P = I x IR P = I2 R (a) 225 W 32 W
2 A 0.2 A 15 Ω 10 000 Ω 7.2 W 4 A 48 Ω P = I V P = (V/R) x V P = V2 / R (a) 20 W 0.5 W 15 V 6 V 20 Ω 132.25 Ω 100 W 7 V 66 Ω (a) 407 Ω 0.57 Ω 11 232 000 J (a) Electrical Heat S1 and S2 4.6 A 1058 W 37.5 Ω 1411 W 63 480 + 677 280 = 740 760 J High current in transmission lines results in high energy loss. Using high voltages reduces the current in transmission lines and therefore reduces energy loss. (a) 0.36 W 10.8 W 900 W Specific Heat Capacity (p58 – 59) Heat is a form of energy. Temperature is a measure of how hot or cold an object is. 4180 J of heat energy is needed to change the temperature of 1 kg of water by 1 °C. (a) 47 000 J 112 750 J 4100 J kg-1 °C-1 270 J kg-1 °C-1 0.4 kg 5.5 kg 7.5 °C 4 °C 752 400 J 380 J kg-1 °C-1 2.5 °C 12 kg (a) 618 J kg-1 °C-1 The experimental value is larger. This is because not all heat energy is absorbed by the copper block. Heat Transfer (p60) (a) Heat energy is transferred by vibrations of particles that are in contact with each other. Particles that are heated rise while particles that have cooled fall. There must be space between particles for this to happen. Heat energy travels in straight in the form of electromagnetic radiation. No particles are required for heat to be transferred by radiation. Despite having a lower temperature, a cup of coffee has more heat energy than a single spark from a sparkler. The tomato has a higher specific heat capacity. More heat energy is required to change its temperature. Fire fighting clothing is made of a substance that is fire resistant and a poor conductor of heat. The clothing is insulated trapped air which prevents heat transfer from surroundings. Reflective panels are used for visibility but also reflect heat radiation. Conduction: a fabric insulating cover on the outside of the boiler prevents heat loss. Convection: The top of the boiler is air-tight to prevent heat loss. Radiation: The interior (or exterior) of the boiler can be coated with a reflective
material (such as foil) to prevent heat loss. Pressure (p61 – 62) Pressure is the force applied to an area of a surface. (a) 75 Pa 8000 Pa 220 000 N 720 N 60 m2 3.5 m2 149 Pa 0.08 m2 (a) 4032 Pa 260 Pa (a) Answer depends on student. Answer depends on student. A person is more likely to fall through an icy lake on tip-toes. The area of contact with the ice is low, so the pressure on the ice will be high. 0.0005 m2 Gas Laws (p63 – 67) When a particle is heated, it vibrates. If it is heated enough, the particle will vibrate enough to break free from surrounding particles. This turns a substance from a liquid to a gas. The particles in the air are moving around all the time. When the air particles collide with the inside surface of the tyre, they impart a force and, therefore, a pressure is created. -273 °C is the temperature at which particles stop vibrating and so, as a result, it’s the coldest possible temperature. (a) 273 K 293 K 0 K 373 K (a) and (b) Pressure is directly proportional to temperature (in Kelvin). As temperature increases, the particles in the gas gain kinetic energy. Therefore, they collide with the sides of the container more often and with more force. This results in a pressure increase. As the tyre heats up during travel, the air particles inside will collide with the inside surface of the tyre more often and with more force. If the pressure gets too high, the tyre could burst. 129 kPa 30 °C (a) Pressure is inversely proportional to volume. As the volume of a gas increases, the particles will hit the sides of a container less often so the pressure decreases. If a balloon is squeezed, the volume of the air inside decreases. Therefore, the pressure of the gas increases and the balloon could burst. 1.68 x 105 Pa