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Half Life

The radioactivity of a sample decreases over time. Half life is a measurement of this decrease.

What is Half life?

The radioactivity of a sample decreases over time. Half life is a measurement in this decrease.The half–life of a radioactive substance is a constant for each radioactive material. It measures the time it takes for a known amount of the substance to become reduced by half due to radioactive decay, and therefore, the emission of radiation.

Half life demo

In this tutorial you will learn how to calculate the half life of a radioactive material.

Chilled practice question

The activity of a radio-isotope is 1536 cpm. What is its activity after five half lives?

Frozen practice question

A radio-isotopes activity falls from 1880 cpm to 235 cpm in 72 minutes. Calculate it’s half life.

Science in context

The radioactivity of a sample decreases over time. Half life is a measurement of this decrease

Millie’s Master Methods

The Fridge Physics Store

Gravitational Potential Energy

Lifting an object in a gravitational field transfers energy into the objects gravitational energy store. Gravitational potential energy is the energy an object has due to its height above Earth.

What is Gravitational potential energy?

Lifting an object in a gravitational field transfers energy into the objects gravitational energy store. Gravitational potential energy is the energy an object has due to its height above Earth. The equation for gravitational potential energy is GPE = mgh, where m is the mass in kilograms, g is the gravitational field strength (9.8 N/Kg on Earth), and h is the height above the ground in meters.

Gravitational potential energy equation

To calculate Gravitational potential energy we use this equation.

$E_p = mgh$

Gravitational potential energy demo

In this tutorial you will learn how to calculate the energy stored in an elevated object.

Chilled practice question

Copy out the question and attempt to calculate the answer before watching the solution. Write down the equation and show all of your working, remember to add the units to your answer, this routine will guarantee you maximum marks in an exam. Mark your solution and correct if needed.

A barrel is lifted onto a shelf 3.5 m from the ground. The barrel has a mass of 22 Kg. Calculate the energy in its G.P.E store.

Frozen practice question

Copy out the question and attempt to calculate the answer before watching the solution. Write down the equation and show all of your working, remember to add the units to your answer, this routine will guarantee you maximum marks in an exam. Mark your solution and correct if needed.

A ski lift transfers 11 KJ of energy into a mans G.P.E energy store. The man has a mass of 55 Kg, calculate the height he was elevated.

Science in context

Lifting an object in a gravitational field transfers energy into the objects gravitational energy store.

Millie’s Master Methods

The Fridge Physics Store

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 equation.

$efficiency = {\text{useful energy output} \over\text{total energy input}}$

Efficiency demo

In this tutorial you will learn how to calculate how efficient a device is at transferring energy from one form to another.

Chilled practice question

Calculate the efficiency of a light bulb with a total input energy of 500 J. The bulb emits 200 J of light energy and 300 J of heat energy.

Frozen practice question

A tumble drier is 80% efficient. Its useful energy is 45 KJ what is the total input energy in Joules.

Science in context

The efficiency of a device is the proportion of the total input energy that is converted to useful energy.

Millie’s Master Methods

The Fridge Physics Store

Energy Transformed

The potential difference between two points is the energy transferred per unit charge. An electrical circuit is an energy transformation device.

What is Energy transformed?

The potential difference between two points is the energy transferred per unit charge. An electrical circuit is an energy transformation device. Energy is provided to the circuit by an electrochemical cell, battery, generator or another electrical energy source. Energy is delivered by the circuit. The rate at which this energy transformation takes place has a great relevance to the design of an electrical circuit for useful functions.

Energy transformed equation

To calculate Energy transformed we use this equation.

Energy = power x time

$ {\mathit E \, \text = \mathit P \mathit t}$

Energy = charge flow x potential difference

$ {\mathit E \, \text = \mathit Q \mathit V}$

Energy transformed demo

In this tutorial you will learn how to calculate the energy transformed through an electrical circuit.

Chilled practice question

Calculate the energy transformed if a circuit is supplied with 6 V and 32 C of charge flows.

Frozen practice question

Calculate the energy transformed when a current of 4 A flows with a p.d of 230 V for 18 s.

Science in context

The potential difference between two points is the energy transferred per unit charge

Millie’s Master Methods

The Fridge Physics Store

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