## OCR Combined Science A – P6/P12

#### Wave Speed

Wave speed is given in meters per second (the number of waves that pass per second). Wavelength is measured in meters and frequency is measured in hertz (Hz), or number of waves per second. Demo In this tutorial you will learn how to calculate the speed of a wave. The equation for this calculation is written like this: $v = { \text f \; \text x \; \lambda }$ Chilled practice question Calculate the velocity of a wave with a wavelength of 6 m and a frequency of 50 Hz Frozen practice question Find the velocity of a wave which has a time…

#### Efficiency

The efficiency of a device is the proportion of input energy that is converted to useful energy. What is Efficiency? The efficiency of a device is the proportion of input energy that is converted to useful energy. Efficiency is a measure of how much work or energy is conserved in an energy transfer, work or energy can be lost, for example as wasted heat energy. The efficiency is the useful energy output, divided by the total energy input, and can be given as a decimal always less than 1 or a percentage. No machine is 100% efficient. Efficiency equation To calculate Efficiency we use this…

#### Transformers

A transformer is an piece of electrical apparatus which will increase or decrease the voltage in an alternating current. It can be designed to “step up” or “step down” voltages and is based on the magnetic induction principle. Demo In this tutorial you will learn how to calculate voltages in step up and step down transformers. The equation is written like this: ${ \text V_{1} \; \text / \; \text V_{2} \; \text = \; \text N_{1} \; \text / \; \text N_{2} \;}$ Chilled practice question A transformer has 300 turns on its primary coil and 100 turns on it secondary coil. What…

#### The Motor Effect

A current-carrying wire or coil can exert a force on a permanent magnet. The force increases if the strength of the magnetic field and/or current increases. This is called the motor effect. Demo In this tutorial you will learn how to calculate the force on a wire carrying a current in a magnetic field. The equation is written like this: $F = { \text B \; \text x \; \text I \; \text x \; \text L}$ Chilled practice question Calculate the force on a wire carrying a current of 3 A. 0.25 m of the wire is in the magnetic field. The magnetic flux density…