Current, Voltage, Resistance and Circuits PDF

14.1, 14.2, 14.3 and 14.4: Current, Voltage, Resistance and Circuits What is electric current? (RECAP) Wire are usually made of copper. Copper wire contains copper ions surrounded by electrons. Those electrons are pushed by external source (Battery) and move along the wire. The...

14.1, 14.2, 14.3 and 14.4: Current, Voltage, Resistance and Circuits What is electric current? (RECAP) Wire are usually made of copper. Copper wire contains copper ions surrounded by electrons. Those electrons are pushed by external source (Battery) and move along the wire. The amount of charges (electrons) flowing per second is called electric current. Measuring electric current (RECAP) Ammeter is a device used to measure the electric current. Unit of electric current = Ampere (A) Series circuits A series circuit is one in which numerous electrical components (Light bulbs) are linked one after the other. There is a single path for the flow of current. (one loop) Parallel circuits The parallel circuit is one in which numerous electrical components (Light bulbs) are linked across one another. The paths are branched for the flow of current. (multiple loops) How to connect ammeter in the circuit? (RECAP) - + Positive terminal of the ammeter is connected to the positive terminal of the battery. Negative terminal of the ammeter is connected to the negative terminal of the battery. Ammeter is always connected in series. Flow of current in series and parallel circuit Current flow in a single loop Current flow in multiple loops/branches Flow of current in series and parallel circuit 1 I1 I1 I I I2 I2 I I 2 I I I I The current is the same The total current is the through out the circuit. addition of all the current in different branches. I = I 1 +I 2 Flow of current in series and parallel circuit 1 2 If one light bulb is broken or blown, If light bulb 1 is broken or blown, the current the circuit is broken (open circuit). still can flow through the other branch. Current cannot flow anymore. Both Light bulb 1 will be off and Light bulb 2 will light bulbs will be off. be on. Control the current flow with switches in circuits 1 1 2 2 Cannot turn the light bulbs Can turn the light bulbs on and on and off separately. off separately. A switch in the circuit can The switch in each branch turn them all on or turn controls the lamps in that branch. them all off. Voltage or potential difference Voltage is a measure of the strength of a cell or battery used to send a current around the circuit. In electrical circuit, battery pushes electrons to flow, and electron gains electrical energy. The size of pushing force depends on the voltage. More batteries  More voltage  More pushing force  More electron flows (More electrical energy)  More current  Lamp will be brighter Voltage symbol: V SI unit of voltage: Volt (V) Measuring voltage or potential difference V V Voltmeter Symbol Voltmeter is used to measure the voltage across the components. If you want to measure the voltage across the bulb, place the voltmeter across the light bulb. V If you want to measure the voltage across the cell, place the voltmeter across the cell. Voltage in series circuits 6V V1 V2 V V 3V 3V The voltage across the components add up to the voltage of the battery. V = V1 + V2 Voltage in parallel circuits 1 Each branch is connected directly to the cell. The voltage across the bulbs is the same as the voltage across the cell. 2 V = V1 = V2 V  Series Vs. Parallel circuit 1 I1 I1 I1 I2 I2 I2 I I 2 I I I I The current is the same through out the The total current is the addition of all the circuit. I = I 1 = I 2 current in different branches. I = I 1 +I 2 The voltage across the components add up to The voltage across the bulbs is the same as the the voltage of the battery. V = V1 + V2 voltage across the cell. V = V1 = V2 A switch in the circuit can turn them all on or The switch in each branch controls the lamps in turn them all off. that branch.  Resistance Resistance is the measure of how much a material opposes the flow of current. The symbol of resistance is R and measured in Ω (Ohms) More light bulbs  Light bulbs are dimmer Difficult for current to flow through the wire. Current becomes smaller. Light bulbs act as resistance against flow of current. 17 Resistance Sometimes we need to make the light dimmer or brighter depending on the situation. In this case, we use device called resistor. Resistor Variable Resistor 19 Resistance in cylindrical conductor (Wire) l Consider water flowing through 2 different pipes. In pipe 1, water cannot flow easily because it is narrow and long Harder for water to flow  High resistance Resistance is directly proportional to the length. In pipe 2, water can flow easily coz it has larger surface area. A Easier for water to flow  low resistance. Therefore, resistance is inversely proportional to the surface area. Resistance is also depends on the types of material. 20 Calculating resistance 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉) 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒(𝑅) = 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐼) SI unit of resistance: Ohm (Ω) SI unit of voltage: Volt (V) SI unit of current: Ampere (A) Calculating resistance What is the resistance of the buzzer? Series circuit  current is the same through out Current passing through the buzzer, I = 0.1 A Only single component in the circuit. Voltage of the battery = voltage across the buzzer, V = 6 V 6V 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 𝑉 6 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑅 = = = 60 Ω 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 𝐼 0.1