S1 Waves & Electricity summary notes

Transcription

1 S1 Waves & Electricity summary notes Waves Reflection and Refraction 1 We are learning to examine what happens to a single ray of light when it hits a plane mirror at an angle. 2 We are learning to examine and draw what happens to a single ray of light as it passes straight through a rectangular block and at an angle. When a single ray of light hits a plane mirror at an angle it will reflect off the mirror at the same angle. Law of reflection: Angle of incidence = Angle of reflection When a single ray of light passes straight through a rectangular block it does not change direction but it does change speed (this cannot be seen but the ray of light will slow down).

2 When a single ray of light passes through a rectangular block at an angle it refracts. This means the ray of light changes speed (slows down) and changes direction as can be seen below. Waves - Concave and Convex Lenses 3 We are investigating ray diagrams for parallel rays of light passing through a concave lens and a convex lens. Convex lenses (converging lenses) will cause the rays to converge to a focus. Concave lenses (diverging lenses) will cause the rays to spread out (diverge). The rays will not come to a focus.

3 Waves - Sight Defects 4 We are exploring how a concave lens and a convex lens can be used to resolve sight defects. A person who is short-sighted can see close-up objects clearly but distant objects will appear blurred. A concave lens can be used to correct this. A person who is long-sighted can see distant objects clearly but closeup objects will appear blurred. A convex lens can be used to correct this.

4 Waves White Light 5 We are investigating what happens to a ray of white light as it passes through a triangular prism. When white light passes through a triangular prism it splits up into 7 different colours called the visible spectrum. This tells us that white light is actually made up of these colours. Red Orange Yellow Green Blue Indigo Violet The same thing happens when white light from the sun passes through rain drops. It splits up into the 7 different colours of the visible spectrum (otherwise known to nonscientists as a rainbow)

5 Electricity Van de Graaff Generator and Circuit Symbols 7 We are investigating the purpose of a Van de Graff Generator. 8 We are considering circuit symbols for various components. How it works: As the rubber belt turns it rubs against a piece of metal connected to the dome. Electrons are released from the rubber belt which build up on the dome. If you are touching the dome the electrons will move onto you. Electrons are negatively charged so they repel each other. This means that all the electrons in your hair are trying to move away from each other and as your hair is very light it stands up. If you touch someone whilst on the Van de Graaff generator the electrons on you can jump to the other person. You both feel a shock and you may see a small spark. This flow of electrons is called an electrical current. The insulation under you and the Van de Graaff generator is there to stop the electrons escaping.

6 Circuit Symbols Switch Lamp Wire/Lead Buzzer Battery Remember that we use circuit symbols because they are much easier and quicker to draw than pictures (like those in the right hand column of the table above).

7 Electricity Connecting Circuits 9 We are learning to explore the main energy changes in a lamp, electric motor and a buzzer. The main energy change for the appliances are as follows: Lamp = Electrical Energy Light Energy Motor = Electrical Energy Kinetic Energy Buzzer = Electrical Energy Sound Energy (Notice how they all convert electrical energy into another form of energy) Electricity Conductors and Insulators 10 We are learning to identify what a conductor is and what it is usually made of. 11 We are learning to identify what an insulator is and what it is made of. This circuit can be used to test a circuit to see if a material is a conductor or insulator. Gap

8 Firstly the material is placed in the gap. If the lamp lights electrical current is flowing so the material must be a conductor. If it doesn t light then no electrical current is flowing so the material must be an insulator. Conductors of electrical current are usually made of metal whereas insulators are made of materials like plastic, wood, glass cloth etc Electricity Current in a series circuit 12 We are learning to investigate the flow of current at different points in a series circuit. A series circuit is where all the components are connected one after the other in line. The circuit below shows two lamps in series with each other. The size of the current can be measured using a meter called an ammeter. A The unit of electrical current is an ampere (A). Ammeters must be placed in series with other components in a circuit as shown below. The current in a series circuit is the same at all points. A 3 A 1 A V 1.5 V i.e. in the circuit shown A 1, A 2 and A 3 are all equal.

9 Electricity Voltage in a series circuit 13 We are learning to investigate what happens to the voltage in a series circuit. The electrical push which the battery gives to the current is called the voltage. The voltage is measured in volts on a voltmeter V Voltmeters are connected across the part of the circuit where the voltage has to be measured. i.e. they are connected in parallel into the circuit as shown below. In a series circuit the total voltage measured across its components adds up to the supply voltage. i.e. In the circuit below V 3 = V 1 + V 2 V 3 V 2 V 1

10 In the previous circuit we can see that there are two batteries connected in series in the circuit, similar to the example below of three batteries in series. When we come across circuits with batteries in series like this we must add them together to find the total voltage supplied. 1.5V 1.5V 1.5V e.g. The total voltage supplied by the batteries in this circuit is found by adding them together. i.e. 1.5v + 1.5v + 1.5v = 4.5v e.g. In this circuit we should notice that the bottom battery is connected the wrong way round. This means we need to subtract 1.5v. i.e. 1.5v + 1.5v + (-1.5v) = 1.5v 1.5V 1.5V 1.5V

11 Electricity Current in a parallel circuit 14 We are learning to investigate the flow of current at different points in a parallel circuit. A parallel circuit is where components are connected across each other. In the circuit below two lamps are connected in parallel. For the parallel circuit below, the current in A 1 and A 4 will both be the same value. If we add A 2 and A 3 the total will equal to both A 1 and A 4.

12 In the circuit opposite we can see that the ammeter readings of I 1, I 2 and I 3 add up to the supply current I s. Electricity Voltage in a parallel circuit 15 We are learning to investigate what happens to the voltage in a parallel circuit. In a parallel circuit the voltage measured by the voltmeters across each branch of the circuit will be exactly the same and equal to the supply voltage. i.e. V 1 = V 2 = V 3

13 In this circuit we can see that the voltage across each lamp in parallel is the same and equal to the supply voltage from the battery.