# Equation which shows the relationship between current power and voltage

### BBC - GCSE Bitesize: Power

Learn about and revise electrical circuits, charge, current, power and resistance with GCSE Bitesize Combined Science. is the rate of transfer of energy between energy stores The energy transferred can be calculated using the equation. To answer this question, the relationship between the voltage and Case 2: If current I = 8 amps V will be = 10/8 Volts so net power = 10 watts. Relationship of the physical and electrical quantities (parameters) Electric voltage V Ohm's law equation (formula): V = I × R and the power law equation ( formula): P = I × V. P = power, I or J (phase angle) between voltage and amperage. Electric The other two values show then how to do the calculation. Formula for.

Each unit of measurement is named after a famous experimenter in electricity: The amp after the Frenchman Andre M. The mathematical symbol for each quantity is meaningful as well. Most direct-current DC measurements, however, being stable over time, will be symbolized with capital letters. Coulomb and Electric Charge One foundational unit of electrical measurement, often taught in the beginnings of electronics courses but used infrequently afterwards, is the unit of the coulomb, which is a measure of electric charge proportional to the number of electrons in an imbalanced state.

One coulomb of charge is equal to 6,,, electrons. Cast in these terms, current is the rate of electric charge motion through a conductor. As stated before, voltage is the measure of potential energy per unit charge available to motivate electrons from one point to another.

Defined in these scientific terms, 1 volt is equal to 1 joule of electric potential energy per divided by 1 coulomb of charge. Thus, a 9 volt battery releases 9 joules of energy for every coulomb of electrons moved through a circuit.

These units and symbols for electrical quantities will become very important to know as we begin to explore the relationships between them in circuits. Ohm expressed his discovery in the form of a simple equation, describing how voltage, current, and resistance interrelate: In this algebraic expression, voltage E is equal to current I multiplied by resistance R.

Using algebra techniques, we can manipulate this equation into two variations, solving for I and for R, respectively: In the above circuit, there is only one source of voltage the battery, on the left and only one source of resistance to current the lamp, on the right. In this first example, we will calculate the amount of current I in a circuit, given values of voltage E and resistance R: Problem The output transformer for your watt push-pull amp weighs 6.

When holding it in your hands, what is the force of gravity pulling it downward?

### BBC Bitesize - GCSE Combined Science - Resistance - OCR Gateway - Revision 4

The force of gravity in newtons is then 3kg 9. The top of your bench is 1. How much work is required to pick up the transformer and place it on the bench?

What if the transformer is sitting on the floor in the next room, which is 20 meters away? Solution We determined in the previous problem that the force of gravity on a 6. The amount of work in joules is then 29N 1. It therefore takes the same amount of work, 35 joules. Voltage Opposite charges attract. If we move a negative electron towards another electron we perform work because we are moving against an opposing force.

## Resistance

Moving two electrons toward two other electrons requires more work because there is more opposing force. We often need a convenient way to describe how much work is required to move charge from one point to another. That concept is voltage. If moving a positive charge from point B to point A requires positive work, then point A is said to have a positive voltage with respect to B. The relationship between the work required in joules, the amount of charge in coulombs, and the voltage in volts is: Since W and Q can be positive or negative, it stands to reason that V can be positive or negative also.

Problem It takes 1.

Notice that this is opposite to the actual electron flow. What is the voltage V across the resistor? Solution 1x electrons represent 1x We therefore conclude that the voltage at A is positive with respect to B by an amount equal to Thus there is a drop of volts across the resistor from the plate supply to the plate.

## Power and efficiency

Power Power is a measure of the amount of work or energy being expended over time. When measured over the period of one second, the number of joules of sonic energy created from an Ampeg SVT with six push-pull power tubes cranked full blast is going to be far more than from a Champ 5E1.

By the same concept it takes no additional work to physically lift your Hiwatt quickly, but it takes more power because the work is performed over a shorter time period. When work is measured in joules and time is measured in seconds, then the power in watts is equal to the total work divided by the total time: Problem It takes you 2 seconds to steadily lift your 6.