Electricity Past Paper PDF

# 9.5 Adding or removing components You need to be careful adding more cells to a circuit. The lamps can be damaged and the wires can get hot. - Adding more cells increases the current when the other components are kept the same. - Removing cells decreases the current when the other components a...

# 9.5 Adding or removing components You need to be careful adding more cells to a circuit. The lamps can be damaged and the wires can get hot. - Adding more cells increases the current when the other components are kept the same. - Removing cells decreases the current when the other components are kept the same. # Adding or removing lamps You saw in Topic 3.5 that lamps change electrical energy to light energy and thermal energy. - Electrons carry electrical energy around a circuit. When the electrons pass through a lamp, the electrons transfer some of their electrical energy to the lamp. The lamp changes the electrical energy into light energy and thermal energy. - Remember that the current is the same at all positions in a series circuit. Putting a lamp in a circuit will make the electrons move more slowly but they move more slowly the whole way around the circuit. - In the circuit with two lamps, each lamp transfers half the energy compared to just one lamp. The lamps will be dimmer. That means they do not shine as brightly. - Adding more lamps decreases the current when the other components are kept the same. - Removing lamps increases the current when the other components are kept the same. # Questions 1. Which statement is true about current in any series circuit? - A. Current decreases around the circuit. - B. Current increases around the circuit - C. Current stays the same around the circuit. - D. Current increases and decreases around the circuit. # 9 Electricity ## Current in a series circuit If you did Think like a scientist: Making predictions about current in Topic 9.3. you may remember that current is the same all the way around a series circuit. - You can think of the electrons in a series circuit like a train. All parts of the train move at the same speed on the track. The back of the train cannot go faster than the front of the train. As soon as one part of the train moves, all of the train will move. - Electrons flow at the same speed in the wires of a series circuit. When electrons start to flow in one part of the circuit, they all start to flow. - That means you can put an ammeter at any position in a series circuit and it will give the same result. - It also means that you can put the same components of a series circuit in a different order and the current will be the same. - Adding components or removing components will affect the current. The effect depends on what components are changed. # Adding or removing cells You saw in Topic 3.5 that cells and batteries are stores of chemical energy. In a complete circuit, the chemical energy gets changed to electrical energy. - That means if you add more cells to a circuit, you have more chemical energy to change into electrical energy in the circuit. - Look at the two circuits. Each component is identical in both circuits. The circuit with two cells has double the electrical energy of the circuit with one cell. - The lamp will be brighter. The ammeter in the circuit with two cells shows that the current is doubled # Questions: 1. Copy the sentences and use words from the list to complete them. - plastic steel aluminium wood and ... - copper is used to make wires for home use. Copper is a good conductor of electricity. Silver is a better conductor of electricity than copper. Suggest why wires for home use are not made from silver. - The drawing shows some types of plugs that are used in different countries. Explain why: - the bodies of the plugs are made from plastic - the pins on the plugs are made from metal. 2. Explain, in terms of particles, the difference between conductors and insulators. # 9 Electricity ## Insulators Electrical insulators are materials that do not allow current to flow through. - Most non-metals, such as plastic, wood, air and cotton, are insulators. - In an insulator, the electrons are not free to move. Because the electrons are not free to move, current cannot flow. Insulators inhibit electron flow. - Insulators are used to keep people safe from electricity. # Conductors Conductors are materials that conduct electricity. - That means conductors allow current to flow. - You saw in Topic 9.1 that electrons move when current flows. Therefore, a conductor is a material in which electrons are free to move. Conductors allow electrons to flow. - All metals are conductors. - Wires that carry electric current are made from metal. - Most wires in houses and schools are made from copper, with a plastic coating. - Wires that cover long distances are usually made from aluminium or steel. These metals are cheaper than copper. - Some circuits, such as those in phones and laptops, do not use wires. The printed circuit board in the bottom right picture has copper tracks instead of wires. The tracks are yellow because the copper is coated with another material. # Questions: 1. Name the unit used to measure current. 2. The diagram shows four different ammeters in four different circuits. Write down the current shown on each ammeter. Include the unit in your answer. 3. Copy the sentence and use words from the list to complete it. Each word may be used once, more than once or not at all. - slower faster electrons atoms - The greater the current in a circuit, the ________ the flow of ________. 4. Marcus has a circuit with a cell, a lamp and a buzzer. He wants to measure the current in the circuit. Which is the correct way to connect the ammeter in this circuit? # 9.3 Measuring the flow of current When electrons move more quickly, the current increases. When electrons move more slowly, the current decreases. - In Topic 9.2 you saw that you can use an ammeter to measure current. - Current is measured in units called amps. Amps have the symbol A. - Look carefully at the ammeters in the picture. They both have two terminals, for wires to be attached. One terminal is red and the other terminal is black. In a circuit, the red terminal of the ammeter must be connected to the positive terminal of the power supply. The red terminal may be connected directly, or through other components, to the positive terminal of the power supply. - Both ends of the ammeter are the same in a circuit diagram. You do not need to show the red and black terminals on the circuit symbol for an ammeter. - Ammeters are always connected in series with other components in a circuit. If the components are connected in series they are all connected end-to-end, one after another, and there are no branches in the circuit. # 9.2 Electrical circuits This circuit contains a cell, a switch and a buzzer. The circuit could be used in a doorbell. If the switch is pushed outside a door, it makes the buzzer sound and attracts attention inside. This circuit contains a cell, a switch, a lamp and an ammeter. The ammeter measures the electric current. This circuit could be used to light a room and measure the current flowing though the circuit. By measuring the current, you could tell if the cell needs to be replaced - a smaller current means the cell is low on stored energy. The lamp would also become less bright, but you might not notice until too late and you find yourself sitting in the dark! # Questions 1. Draw the circuit symbol for: - a lamp - a cell - a buzzer - a closed switch. # 9 Electricity ## Circuit diagrams Circuits can be shown in a drawing or a circuit diagram. ### Advantages of circuit diagrams compared with pictures: - Circuit diagrams are easier to draw. - The components have standard symbols. - Wires are drawn with straight lines, which is easy to interpret. ## Circuit symbols Components in circuits can look very different. - The picture shows how different some lamps can look. - Standard circuit symbols are used in circuit diagrams so there is no confusion. The same symbols are used in all countries. | Name | Symbol | Function | |-------------|---------|-----------------------------------------------------| | Ammeter | A | measures current in the circuit | | Cell | | provides energy to make current flow | | Lamp | | gives out light | | Switch (open) | | stops the flow of current when opened | | Switch (closed)| | starts the flow of current when closed | | Buzzer | | makes a buzzing sound | # 9 Electricity ## More about electrons - Some of the electrons in a metal are free to move. That means they can move through the metal. - In a metal, these electrons move randomly, as shown in the diagram. - When the metal is placed into a circuit, all the electrons move in the same direction. - Electrons have a negative charge. - Opposite charges attract, and like charges repel. To attract means to pull together and repel means to push apart. That means: - positive and negative attract - positive and positive repel - negative and negative repel. - Therefore, electrons will be attracted towards the positive terminal of the power supply and be repelled from the negative terminal. - If there is a break in the circuit, all the electrons stop flowing. - Electrons can only flow in a complete circuit. # Questions: 1. Name the particles that move around a circuit when current flows. 2. Copy the sentences and use words from the list to complete them. Each word may be used once, more than once or not at all. - attracted repelled positive negative electrons atoms - Current in a circuit is the movement of _____. - These particles have a _______ charge. - These particles are _______ by the positive terminal of a battery and _______ by the negative terminal of a battery. # 9.1 Flow of electricity ## Current - Look at the circuit in the picture. - When you close the switch, the lamp lights. - A cell stores chemical energy that can be changed to electrical energy in a circuit. - A battery contains two or more cells joined together. - The cell in the circuit has two connections, called terminals. - All cells, batteries, power supplies and many other components have two terminals. - The terminals are labelled with + and - symbols, meaning positive (+) and negative (-). - You can see these symbols in the photograph of these three cells. - The photograph below shows one of the batteries from an electric car. You can see that the battery is made from many cells. - When connected into a circuit, the negative terminal of a cell, battery or power supply pushes electrons around in the wires. - All materials contain atoms. Atoms contain smaller particles. An electron is one type of smaller particle in an atom. - The flow of electrons in the circuit is called current. - The flow of current in a circuit is the movement of electrons around the circuit.