Energy transfers (2.4) (M) Flashcards
(25 cards)
The greater the current/potential difference, the (…) the power transfer in the circuit
greater
Everyday electrical appliances are designed to bring about what?
energy transfers
The longer you leave a light bulb on, the (..) the energy is used
greater
2 things
The amount of energy an appliance transfers depends on what?
how long the appliance is switched on for and the power of the appliance
P = E/t
How do different domestic appliances transfer energy from batteries or ac mains to the kinetic energy of electric motors or the energy of heating devices
from chemical store of batteries/electrical store of ac supply to thermal/kinetic store of heating device/electrical motor via work done when current flows
When is work done in a circuit?
when charge flows
The greater the voltage/charge, the (…) the energy transferred/work done.
greater
Describe the relationship between an appliance with a higher power rating and changes in energy store
A device with a higher power rating will transfer stored energy to other types of energy at a faster rate
What are some common power ratings of domestic electrical appliances?
- A kettle is typically 3kW (3000W)*
- A microwave 900W*
- A lightbulb 10W*
- Every appliance in your home will have a power rating on it.*
What is the National Grid?
a system of cables and transformers linking power stations to consumers
National grid only consists from step-up transformer to step-down transformer (does not include houses/power station)
What is used to transfer electrical power from power stations to consumers?
the National Grid
What does a step-up transformer do?
Increase voltage, decrease current
What does a step-down transformer do?
decrease voltage, increase current
What is the role of step-up transformers in the National Grid?
Step-up transformers are used to increase the potential difference (to a very high voltage) from the power station to the transmission cables for efficient transmission
also means thinner wires can be used and less power is lost as P = I2R - add high current stuff to this answer if asked in an exam
What is the role of step-down transformers in the National Grid?
Step-down transformers are used to decrease, to a much lower value, the potential difference for domestic use (as high voltage is unsafe)
Why do transmission cables not have a high current?
If you have a big current then the wires will get hot and lots of (thermal) energy will be wasted
therefore it is very inefficient
so they transmit it at a very high voltage as it makes up the majority of the distance of transmission
The National Grid is an (…) way to transfer energy
efficient
Why is there not a high voltage for domestic appliances?
A high voltage is unsafe - would be fatal
Why could an 18V battery not be used at the input of a transformer?
Need a.c.
Battery is d.c.
Why does the resistance of bulb increase as pd increases across the bulb?
Temperature of bulb increases
2 marks
A small community in the area live in the mountains.
Why would it not be economical to connect them to the national grid?
- high cost of installing overhead power lines or underground cables or pylons
- high cost as (very) long cables needed
- amount of electricity required is too low
4 marker
A man touches a live wire, he experiences an electrical shock, explain why?
The potential difference of the man is 0V
The potential difference of the live wire is 230V
So there is a large potential difference between the man and live wire
so charge passes through his body
top two points unlikely to be needed, possibly need to know bottom two though
What does potential difference mean?
The work done/energy transferred per coulomb of charge
3 marks
Why does the resistance of a metal filament inside a bulb increase as pd increases?
Metals contain free electrons
As the temperature of the filament increases, the ions vibrate faster
so electrons collide more frequently with ions
