Controlling and using Electric Currents

Controlling and using Electric Currents

1. Current & Voltage

   • Size of a current is measure using an ammeter in a series circuit
     • Ammeter- An instrument that measures electric current Series Circuit- Circuits in which the current flowing is the same throughout.
     • Electrons are not used up, and current leaving the cell is the same as current that flows back into cell, so ammeter can be placed anywhere in a series circuit.
     • In a parallel circuit the current splits when it reaches a junction.
       • Parallel Circuit- The current divides into two at a junction.
   • To change the size of current in a circuit, you could change the potential difference (voltage). The higher the potential difference, the bugger the current.
     • Potential Difference- the difference of electrical potential between two points in a circuit.
   • The potential difference is a way of measuring the amount of energy transferred to a component by current. Its measure with a voltmeter, which is placed in parallel with the component. Measures difference between electrons going in and electrons going out.
     • Measures difference between energy transferred to a component for each unit which passes through that component. As energy is measure in joules and charge in coulombs, 1 volt= 1 joule per coulomb

2. Changing Resistances

   • The size of the current depends on the resistance as well as the voltage. The resistance is measured in ohms (Ω)
     • Resistance- How easy or difficult it is for a current to flow around somethng
     • The resistance of the whole circuit depends on the resistances of the components on the circuit, the higher the total resistance the smaller the current.
       • If a resistor remains at a constant temperature, the potential difference, current and resistance are linked by this equation: potential difference (Volts,V)= Current (Amperes, A) x Resistance (Ohms, Ω)
   • The resistance can be changed by using a different resistor or by using a variable resistor.
     • Filament Lamp- Heat up when being used. A higher potential difference makes them hotter, and as they get hotter the resistance gets greater.
       • Increasing gradient shows that a filament lamp is a non-ohmic resistor as current isn't directly proportional to resistance.
     • Wire- Heats up when being used, as voltage increases. Resistance increases as wire gets hotter.
       • An ohmic converter which is shown by the constant gradient, meaning that the increase in current in voltage are proportional so increase in resistance will be too. Follows ohm's law.
     • Diode- When in reverse bias, it prevents the lamp from lighting, whereas in forward bias the lamp is lit. The current only flows in one direction, when a diode is being used. This means you can block half an alternating current.
       • As the voltage increases the resistance will suddenly will suddenly decrease and the current flows. Gradient highers as the resistance decreases. Non-ohmic as current and voltage aren't proportional
     • Thermistor- As the temperature increases the resistance decreases, they are an electronic component that respond to an environmental change. They can be used to turn on cooling devices, in heating systems or in kettles.
       • Downward curve becomes less steep as the temperature increases shows that the resistance decreases as temperature increases.
     • LDR- Stands for light dependent resistor. LDRs are components which depend on light intensity. If the light intensity is high the resistance will decrease, and more current will flow, and if light intensity is low resistance will increase, and less current will flow. This means LDRs can be used as switches.
       • The line of best fit is a curve which demonstrates that the resistance decreased at and almost constant rate as the light intensity bettered. This is because an LDR's resistance will increase as if the light intensity is high whereas it will decrease if light intensity is low.

3. Transferring Energy

   • When current flows through a resistor, energy is transferred to the resistor and it becomes warm. This is useful in electric fires such as kettles and electric fires. These appliances are basically large resistors.
     • A similar thing happens with all components- even components such as motors where the main energy transfer us from electrical to kinetic energy. In the case of a motor, the heat produced is wasted energy. Some electrical appliances produce so much waste heat energy that they burn people.
       • A current in a wire is a flow of electrons, as the electrons move in a metal they collide with the ions in the lattice and transfer some energy to them.
   • Power is the energy transferred every second. For electrical appliances the power can be worked out from the current and potential difference. The unit of power per second or watts (W) (1 watt- 1 joule/second).
     • electrical power (watts)= current (amperes) x potential difference (volts). P=IxV
     • The total energy transferred by an appliance depends on its power and for how long it is switched on for. The energy transferred can be calculated with this equation
       • Energy transferred = current(A) x potential difference (V) x time (seconds). E=I x V x t

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