Electricity Knowledge Organiser

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across the gap- this is the spark. attraction repulsion repulsion Electric charges create an electric field. The closer you get to the object, the stronger the field. The electric field can be shown by drawing field lines, they go from positive to negative. ** If a charged object is placed near the field, it will experience a force. The force becomes stronger as the charged object gets closer. Resistance voltage (V) = current (A) x resistance (2) V = IR Graphs of I-V Characteristics for Components in a Circuit 1. Ohmic conductor: the current is directly proportional to the potential difference - it is a straight line (at a constant temperature). 2. Filament lamp: as the current increases, so does the temperature. This makes it harder for the current to flow. The graph becomes less steep. 3. Diode: current only flows in one direction. The resistance is very high in the other direction which means no current can flow. Current and Circuit Symbols Current: the flow of electrical charge. cell Potential difference (voltage): the push of electrical charge. Resistance: slows down the flow of electricity. resistor battery HH 办 variable resistor open switch closed switch ammeter A voltmeter bulb Current I in amps A diode Current fuse LDR LED thermistor en V in volts ( Valtage Potential Derece Electricity - Separate Science Circuit Devices LDR - Light Dependent Resistor An LDR is dependent on light intensity. In bright light the resistance falls and at night the resistance is higher. Uses of LDRs: outdoor night lights, burglar detectors. Resistance (in Ohms) Light Dependent Resistor (LDR) Thermistor Light Intensity A thermistor is a temperature dependent resistor. If it is hot, then the resistance is less. If it becomes cold, then the resistance increases. resistance (ohms) Uses of thermistors: temperature detectors. temperature (°C) Series and Parallel Circuits Series Circuits Once one of the components is broken then all the components will stop working. Potential difference - the total p.d. of the supply is shared between all the components. Current wherever the ammeter is placed in a series circuit the reading is the same. Resistance - In a series circuit, the resistance will add up to make the total resistance. Parallel Circuits They are much more common - if one component stops working, it will not affect the others. This means they are more useful. 0 Calculating Charge charge flow (C) = current (A) x time (s) Q = It V total = V₁ + V₂ 1₂ = 1₁₂ = 1₂ potential difference - current x resistance V (V) = I (A) x R (0) Rotal = R₁ + R₂ Potential Difference - this is the same for all components. V₁ = V₂ Current the total current is the total of all the total = 1₂ + 1₂ + 1₂ currents through all the components. Resistance adding resistance reduces the total resistance. HHH Charge Electric current is the flow of electric charge. It only flows when the circuit is complete. The charge is the current flowing past a point in a given time. Charge is measured in coulombs (C). Electricity in the Home AC - alternating current. Constantly changing direction - UK mains supply is 230V and has a frequency of 50 hertz (Hz). DC - direct current. Supplied by batteries and only flows in one direction. Cables- most have three wires: live, neutral and earth. They are covered in plastic insulation for safety. earth wire neutral wire outer insulation Step-up transformers - increase the voltage as the electricity flows through the cables. live wire Live wire - provides the potential difference from the mains. Neutral wire - completes the circuit. Earth wire - protection. Stops the appliance from becoming live. Carries a current if there is a fault. Step-down transformers decrease the potential difference to make it safe. fuse Touching the live wire can cause the current to flow through your body. This causes an electric shock. cable grip Energy Transferred this depends on how long the appliance is on for and its power. E = Pt energy transferred (J) = power (W) x time (s) Energy is transferred around a circuit when the charge moves. energy transferred (J) = charge flow (C) x potential difference (V) power (W) = potential difference (V) x current (A) P = VI P = I²R power (W) = current² (A) x resistance (2) The National Grid The National Grid is a system of cables and transformers. They transfer electrical power from the power station to where it is needed. Power stations are able to change the amount of electricity that is produced to meet the demands. For example, more energy may be needed in the evenings when people come home from work or school. Electricity is transferred at a low current, but a high voltage so less energy is being lost as it travels through the cables. E = QV