Physics- Current and Voltage

• Electrical current is the amount of charge that passes a point in a conducting wire every second
• The symbol for current is “
• Electric current is measured in amperes (A) or milliamperes (mA)
• An instrument used to measure very weak electric current is called a galvanometer
• Larger currents are measured with an ammeter or milliammeter
• Energy for pushing electrons is available if positive and negative charges are separated
• A battery forces electrons to accumulate at one terminal, making it negatively charged
• Electrons withdraw from the other terminal, leaving it positively charged
• All forms of energy are measured in joules (J)
• When describing the energy of electrons in an electric circuit, we describe the energy possessed by a standard unit of charges instead of the total energy of all the charges
• We always compare one point in a circuit to another
• Potential difference means the difference in energy per unit of charge between one point in the circuit and another point in the circuit
• Potential difference is commonly referred to as Voltage
• The standard unit for potential energy is the Volt (V)
• Most electrical devices require potential differences of 1 to 120V
• Voltage is measured with a Voltmeter, represented by a V with a circle around it
• Resistance is the property of a substance that hinders the motion of electrical charge and converts electrical energy into other forms of energy
• In a circuit, current is the movement of electrons through conductors, voltage is what drives the movement of electrons, and resistance is what opposes the motion of the electrons
• A good conductor, like copper, allows electric charge to move easily through it, resulting in low resistance
• A poor conductor, like rubber, hinders the movement of charge, resulting in high resistance
• The standard unit for resistance is the Ohm (Ω)
• Electronic devices contain resistors with a range of values from milliohms to megaohms
• Resistance can be measured with an ohmmeter
• Resistance affects current flow and the potential difference between different points in a complex circuit with multiple loads
• Electrical resistance is calculated by finding the ratio of the voltage across the load (V) to the current through the load (I)
• Units for resistance are volts per ampere (V/A) which is equivalent to ohms
• The equation for calculating resistance is called Ohm’s Law and can be rearranged to find any variable
• Resistors are used to control current or voltage to suit the specific needs of other electronic devices in the circuit
• Circuit resistors are typically made of a heat-conducting ceramic core coated with materials such as carbon, metal oxides, metal film, or resistance wire
• Modern “chip” resistors are very small and mounted directly on the surface of the board
• Variable Resistors don’t have a fixed resistance as the resistance can change based on its response to temperature, light, voltage, or other variables
• Nichrome wire is a variable resistor as changing the length of the wire can change the resistance
• Variable resistors are used in light dimmers, refrigerator, and stove temperature controls