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Resistance

Resistance is an electrical quantity that measures how a device or material reduces the electrical current flow through it.

What is Resistance?

Resistance is an electrical quantity that measures how the device or material reduces the electrical current flow through it. Resistance is measured in ohms (Ω).If we make a comparison of resistance to water flow in pipes, the resistance is greater when the pipe is thinner, so the water flow is decreased It slows down which also happens to the flow of electricity.

Resistance equation

To calculate Resistance we write the equation like this.

$V = { \mathit I \, \mathit R} $

Resistance demo

In this tutorial you will learn how to calculate the resistance in an electrical circuit.

Chilled practice question

Calculate the resistance of a bulb supplied with 8 V and a current flow of 2 A.

Frozen practice question

Calculate the current in a circuit which has a resistance of 16 Ω and a potential difference of 8 V.

Science in context

Resistance reduces the flow of electricity.

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Resistance in Series and Parallel

Resistors in series and in parallel can change the total resistance in a circuit.

What is Resistance in series and parallel?

Resistors in series and in parallel change the total resistance in a circuit. Special components called resistors are made especially for creating a precise quantity of resistance in a circuit. They are generally made of metal wire or carbon and constructed to maintain a stable steady amount of resistance over a wide range of environmental conditions.

Resistance in series and parallel equation

To calculate Resistance in series we use this equation.

$R_t = {\mathit R_1 \text + \mathit R_2}$

Resistance in series and parallel demo

In this tutorial you will learn how to calculate the total resistance of resistors in series and parallel.

Chilled practice question

Calculate the current in a circuit if it is supplied with a voltage of 36 V and has two resistors in series one 6 Ω and the other 3 Ω.

Frozen practice question

Three resistors are connected in parallel, resistor A is 2 Ω , resistor B is 4 Ω, and resistor C is 5 Ω . What is the total resistance in the circuit ?

Science in context

Resistance in series and parallel change the total resistance in a circuit

Millie’s Master Methods

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Electrical Power

The power of an appliance is the energy that is transferred per second. Electric power is the rate, per unit time at which electrical energy is transferred by an electric circuit.

What is Electrical power?

The power of an appliance is the energy that is transferred per second. Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The unit for power is the watt, which is the transfer of energy at the rate of one joule per second. Electric power can be produced by electric generators and batteries.

Electrical power equation

To calculate Electrical power we use this equation.

$ {\mathit P \, \text = \mathit V \mathit I}$

Electrical power demo

In this tutorial you will learn how to calculate the electrical power of an electrical appliance.

Chilled practice question

Calculate the power in a circuit when a p.d of 18 V and a current of 4 A is measured.

Frozen practice question

Find the current flowing through an appliance which has a power rating of 14 KW and a p.d of 230 V.

Science in context

The power of an appliance is the energy that is transferred per second

Millie’s Master Methods

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Density

Density is a measure of how compact the particles are in a substance. Density is defined as the mass per unit volume.

What is Density

Density is a measure of how compact the particles are in a substance. Density is defined as the mass per unit volume. It is mathematically defined as mass divided by volume: ρ = m/V. The density(ρ) of a substance is the total mass (m) of that substance divided by the total volume (V) Of the substance.

Density equation

To calculate Density we use this equation.

${\rho} = {\text{m} \over\text{V}}$

Density demo

In this tutorial you will learn how to calculate the density of different substances.

Chilled practice question

A block has a mass of 20 Kg and a volume of 0.25 m3. Calculate its density.

Frozen practice question

A barrel has a mass of 2500 g and a density of 2 Kg/m3. Calculate the barrels volume.

Science in context

Density is a measure of how compact the particles are in a substance.

Millie’s Master Methods

The Fridge Physics Store

Specific Latent Heat

Specific latent heat is the energy needed to change the state of a substance.

What is Specific latent heat?

Specific latent heat is the energy needed to change the state of a substance. Latent heat is the energy absorbed or released by a substance during a change in its physical state. The latent heat is normally shown as the amount of heat energy in joules per Kg mass of the substance undergoing the change of state.

Specific latent heat equation

To calculate Specific latent heat we use this equation.

$E = {\text{m} \text{L}}$

Specific latent heat demo

In this tutorial you will learn how to calculate the energy needed for different substances to change their state of matter.

Chilled practice question

The specific latent heat of water for melting is 334000 J/Kg. How much heat energy needed to melt a 30 Kg block of ice ?

Frozen practice question

What is the specific latent heat of a material if 2 Kg of the material releases 95.5 KJ of energy when it melts ?

Science in context

Specific latent heat is the energy needed to change the state of matter a substance.

Millie’s Master Methods

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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

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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

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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

Forces and Work Done

The unit for work done is the joule (J), or Newton meter (N-m). One joule is equal to the amount of work that is done when 1 N of force moves an object over a distance of 1 m.

Demo

In this tutorial you will learn how to calculate the work done to move an object through a known distance.

Note-Some mobile devices may require you to tap full screen during playback to view video content.

The formula for this equation is written like this:

w = f x d

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.

How much work has been done if a car is pushed along the road 550 cm with a force of 400 N ?

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.

75 J of work is done pulling a trolley 150 cm. Calculate the force applied.

Science in context

Work can be calculated with the equation: Work = Force × Distance. The unit for work is the joule (J), or Newton • meter (N • m). One joule is equal to the amount of work that is done when 1 N of force moves an object over a distance of 1 m.

Millie’s Master Methods

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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 voltage is induced in the secondary coil if the primary voltage is 96 V ?

Frozen practice question

A transformer has 320 turns on the primary coil and 800 turns on the secondary coil. Find the voltage across the primary coil when the voltage across the secondary coil is 1320 V.

Science in context

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.When a voltage is introduced to one coil, called the primary coil it magnetizes its core which is made from iron which induces a voltage in the secondary coil.

Millie’s Master Methods

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