CH 16: Current of Electricity

• An electric circuit is a complete or closed path through which electric charges can flow from one terminal of an electrical source to another, passing through one or more electrical components.
• The four main components in an electrical circuit are the electrical energy source or active components, the load or passive components, the conductors which connect components together, and the switches which are used to close or open a circuit.
• Electrical energy source or active components in an electric circuit include horizontal battery, EC or AC source, and load or passive components include lamb, solar energy heater, speaker, and motor.
• Conductors in an electric circuit include copper wires.
• Switches in an electric circuit include button switch and two-way switch.
• Electric current is the rate of flow of electric charge, represented by the formula i equals q over t, where i is the electric current, q is the electric charge, and t is time.
• The SI unit for electric current is ampere, symbol capital A.
• An ammeter is used to measure current and should be connected in series with other components if it is connected in parallel it will cause a short circuit.
• Conventional current is the flow of negative charges that is electrons from negative terminal to positive terminal of the energy source.
• Electromotive force or emf symbol epsilon is work done w by the source to move one unit of charge q around a complete circuit, represented by the formula epsilon equals w over q.
• Potential difference or pd symbol v is work done w to move one unit of charge q through two points, represented by the formula v equals to w over q.
• A voltmeter is used to measure emf or pd between two terminals and should be connected parallel in a circuit it is an open circuit if it is connected in series.
• Electromotive force is related to energy sources, for example, battery, lead or dc supply, while potential difference is related to loads, for example, light bulbs and resistors.
• Energy sources provide energy to the circuit, while loads consume energy from the circuit.
• In an experiment to determine unknown resistance, a real estate is set to maximum value to allow a small amount of current flowing, protecting the circuit from excess current.
• The gradient of the graph obtained from the recorded emitter reading i and corresponding voltmeter reading v can be used to determine the unknown resistance r.
• The switch is closed to allow current flowing through the circuit, and the emitter reading i and the corresponding voltmeter reading v are recorded.
• Ohm's law states that the current i flowing through a metallic conductor is directly proportional to the potential difference v across it under constant physical conditions.
• Resistivity rho is an intrinsic property of a material and is a measure of how much material resists the flow of electric current.
• In the reverse bias region, when the voltage applied on the diode is reverse, the diode has very high resistance and very small amount of current flows in opposite direction.
• The gradient on the graph obtained from the recorded emitter reading i and corresponding voltmeter reading v indicates the resistance of the filament lamp.
• Variable resistors are resistors that can be changed within a range.
• In the forward bias region, when the voltage applied on the diode is more than vf, the diode has very low resistance and becomes a conductor, allowing a large amount of current to flow.
• A diode allows current to flow in one direction only, and its iv curve is shown below.
• The resistance of a uniform wire is directly proportional to its length l and inversely proportional to its cross-sectional area a.
• The red state is adjusted to allow more current flowing through the circuit, and another set of emitter reading i and corresponding voltmeter reading v are recorded.
• The formula for the resistor is r equals rho l over a where rho is the resistivity of the material.
• Fixed resistors are resistors that have constant resistance.
• There are two types of resistors: fixed resistance and variable resistance.
• Energy sources convert other forms of energy, for example, chemical energy to electrical energy, while loads convert electrical energy to other form of energy, for example, light and heat.
• Resistance symbol r is a measure of the extent of the component resist the flow of electrical charge, represented by the formula r equals to v over i.
• Resistors are components with known resistance value and are used to control the amount of electric current.