Physics

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  • Created by: IJM22
  • Created on: 16-01-19 16:18
What happens when electrons pass through a component?
The electrical energy is transferred into different forms of energy
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What happens to all the electrical energy carried by the current?
The current is transferred by the lamp into other forms of energy
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How do electrons move?
They collide with atoms in the metal.
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What other energy can electrical energy be transferred into?
Thermal
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What does the resistance tell us?
Tells us the potential difference needed to drive a current through a component
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hh
v2 (m/s2)
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What is the energy change when a car is travelling at a constant speed?
Chemical store in energy → Kinetic energy store
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Example 1: A car with a mass of 700kg is moving with a speed of 20m/s. Calculate the kinetic energy of the car
1) Ek = 0.5 × m × v2 2) Ek = 0.5 × 700 Ek
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Example 2: A cyclist and bike have a total mass of 100kg and a speed of 15m/s. Calulate the kinetic energy,
1) Ek = 0.5 × m × v2 2) Ek = 0.5 × 100 ×V2 3) = 11,250 J/1000 = 11.25 KJ
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What happens when we stretch a spring?
We apply a force to change the length of the spring
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What is the scientific word for applying a force?
'work'
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What is it called when a stretched spring is storing energy?
Elastic potential energy
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What is the strectch called when we apply a force?
Extension
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What is the symbol for extension
Lowercase 'e'
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What is it called when the spring has been strecthed beyond the limit?
Limit of proportionality
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What is the equation for elastic potential energy?
Ee = 0.5 × k × e2
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What is gravitational potential energy?
Energy stored in an object due to its position above the Earth's surface
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What is the formula for gravitational potential energy?
Ep = m × g × h
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Example 1 of gravitational potential energy: A crane lifts 75kg mass a height of 8m. Calculate the gravitational potential energy gained by the mass (g = 9.8kg)
1) Ep = m × g × h 2) Ep = 75 × 9.8 × 8 = 5880
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Example 2 of gravitational potential energy: A ball with a mass of 500g is lifted onto a shelf which is 1.5m above the ground. Calculate the gravitational potential energy gained by the ball (g = 9.8 N/kg)
First convert 500g into kg by dividing by 1000. 1) Ep = m × g × h 2) 0.5 × 9.8 × 1.5 = 7.35J
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What is the specific heat capacity?
The amount of energy required to raise the temperature of 1kg of the substance by 1° C
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What is the equation for specifc heat capacity?
E = m × c × O (change in temperature)
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Example 1 of specific heat capacity:
Calculator the energy required to increase the temperature of 2kg of water from 20° C to 100° C. The specific heat capacity of water is 4200 J/kg° C
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Example 2 of specific heat capacity:
An iron has an aluminium plate with a mass of 1.5 kg. Calculate the thermal energy stored in the plate when the temperature rises from 20° C to 200° C. The specific heat capacity of aluminium is 913J/Kg° C
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Example 3 of specific heat capacity:
A hot water bottle cools down from 80° C to 20° C, releasing 756000 J of thermal energy. Calculate the mass of the water in the hot water bottle. The specifc heat capacity of water is 4200 J/kg° C
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What is work?
Whenever energy is transferred from one store to another
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What does mechanical work involve?
Using a force to move an object
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What does electrical work involve?
A current transferring energy
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What is the equation for work done?
Work done (J) = Force (N) × Distance (m)
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Example 1 of work done by force: During braking, a force of 2000N is applied to the brakes of a car. The car takes 20 m to come to a stop. Calculate the work done.
1) Work done (J) = Force (N) × Distance (m) 2) 2000N × 20 m = 40,000 J
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What is power?
The rate at which energy is transferred or the rate at which work is done
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What is the first equation for power?
Power (W) = Energy transferred (J)/ Time
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What is the second equation for power?
Power (W) = Work done (J)/ Time (s)
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What is the formula for effciency?
Efficiency = useful output energy transfer/ total input energy transfer
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What is the second formula for effciency?
Effciency = useful power ouput/total power input
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Example 1 of effciency: An electric hot is used to heat water.15,000 J of thermal energy is transfered by the hot. 12,000 J of thermal energy passes into the water. Calculate the efficiency of energy transfer into the water
1) Efficiency = useful output energy transfer/ total input energy transfer = 12,000 J/15,000 = 0.8
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Example 2 of effciency: An electric current delivers a power of 60 watts to a light bulb. 3 watts of electrical energy are transferred to light energy. Calculate the efficiency of the bulb
1) Effciency = useful power output/ total power input = 3/60 = 0.05
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What are the two main factors when it comes to thermal conductivity
The higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across that material
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What layers are modern houses built from?
External brick and internal breezeblock
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What is between the walls with houses?
Cavity
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Why do builders pack in between walls and why?
They pack cavity as it has a low thermal conductivity
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Why do most houses have double glazed windows?
As there is low thermal conductivity
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Name one way thermal energy can escape through the house?
The roof of a house
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How can you reduce thermal energy from escaping the house?
By placing it with loft insulation
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What does loft insulation have?
A low thermal conductivity which reduces the rate at which thermal energy passes through
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Name some ways to reduce thermal energy transfer from a house?
Construct the building using materials with a low thermal conductivity and build the house with thick walls as it reduces the rate of thermal energy transfer
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Other cards in this set

Card 2

Front

What happens to all the electrical energy carried by the current?

Back

The current is transferred by the lamp into other forms of energy

Card 3

Front

How do electrons move?

Back

Preview of the front of card 3

Card 4

Front

What other energy can electrical energy be transferred into?

Back

Preview of the front of card 4

Card 5

Front

What does the resistance tell us?

Back

Preview of the front of card 5
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