Physics Flashcards
Whats happens when two objects are rubbed together in static electricity?
The electrons move from one object to another causing one object to have an overall positive charge and the other object to have an overall negative charge.
Like charges repel
Unlike charges attract
Neutral objects are attracted to both positively and negatively charged objects.
How would you test if an object is charged?
You could check if it attracted bits of paper, hair, etc. It could attract or repel another charged object.
What happens if an object becomes highly charged?
If an object becomes highly charged then the potential difference between the object and the ground increases and the object will discharge. When a charged object discharges (goes to the ground) then a spark might occur. This is the electrons jumping from the object to the earthed conductor.
What is current?
Current (I) is the rate of flow of electrical charges or electrons. For example, the number of charges per second. In other words: Current is the amount of charges (measured in Coulombs) that flow every second, it is represented by the equation:
Current (Ampere, A) = Charge (Coulombs, C) ÷ Time (s)
So if a circuit has a current of 2A that means that there are 2 coulombs of charge going around the circuit every second.
A quick example to the last card: 6 Coulombs of charge go around a circuit every 2 seconds. What is the current?
I = Q ÷ t I = 6C ÷ 2s = 3A
What is voltage or potential difference (symbol V, measured in volts, v)
The amount of energy transferred by the charges. For example, the amount of energy per charge
How do you calculate potential difference/voltage?
To calculate potential difference/voltage you use the following equation:
Work done (J)
–––––––––––
Charge (C)
If there is a 2V cell or battery in a circuit then it gives 2 joules of energy to every coulomb of charge. When these charges get to the device in the circuit e.g. a bulb, then the energy gets transferred to the device.
What is resistance?
Resistance is something that opposes the flow of current.
Voltage, current, and resistance, related by the equation: V = I x R
What do current-potential difference graphs tell you?
How the current through a component varies with voltage.
What are the two types of circuits?
Parallel and series circuits.
In a series circuit:
• The total resistance is the sum of the resistance of each component in the circuit
o Total resistance (R-total) = R1 + R2
• The current is the same at every point in the circuit
• The voltage is shared between each component in the circuit
o Total voltage (V-total) = V1 + V2
In a parallel circuit:
• The voltage is the same across each branch
o V-total = V1 = V2
• The total current through the circuit is the sum of the current through each component
o Total current (I-total) = I1 + I2
What are the two types of current in a circuit
Direct current and alternating current.
What is direct current?
Current that only flows in one direction.
In circuits that are powered by cells/batteries the current only flows in one direction, this is called direct current (d.c.)
What is alternating current?
Current that changes direction. Ex. the current move back and forth in the circuit.
Alternating current (a.c.) is what we receive from the power station and what comes out of plug sockets.
What happens to a fuze if the current exceeds the rating?
It will blow.
What are the three most common fuze ratings?
3A, 5A, and 13A
How do you know what rating of fuse to use?
You need to know the electrical power of the device.
How do you calculate power?
Power (W) = current (A) x potential difference (V)
Important thing on fuses
If an electrical fire has a power rating of 1150W and the voltage used is 230V then what fuse should be used?
Rearranging the equation we get:
I = P ÷ V
I = 1150 ÷ 230
= 5A
(practice the above with different numbers)
The fuse that should be used is 13A because if a 3A or 5A fuse was used then it would ‘blow’ even if the device was working correctly.
What does a magnet have?
A magnet always has a north pole and a south. A material which has its electrons very aligned will have properties of magnetism. These properties include the ability to attract other magnets.
Is the Earth a magnet?
Yes. The earth has a north pole and a south pole like a magnet.
Why is the earth considered a magnet?
- The core is magnetic and creates a large magnetic field around the Earth
- We know this because a freely suspended magnetic compass will align itself with the earth’s field lines and point North
- It doesn’t point to the Geographic North pole – it is over North Canada
- Also, the compass is effectively a suspended Bar Magnet, with its own north pole lining up with Earth’s ‘North pole’
o However this cannot be right, as like poles repel
o So in fact, Earth’s magnetic pole above Canada is the magnetic South Pole! (and the geographic south pole is close to the Magnetic North Pole)
What are four magnetic substances that can be attracted by a magnet>
Nickel, Steel, Iron, and Cobalt
What are the properties of magnetically hard and soft materials?
Hard magnetic materials stay magnetized for much longer, soft magnetic materials don’t stay magnetized.
What is the difference between magnetically soft materials and magnetically hard materials?
Magnetically soft materials are easy and quick to magnetize and demagnetize. They lose their magnetic properties very quickly once they have left a magnetic field.
Magnetically hard materials keep their magnetic properties for a long period of time/permanently, magnetically hard materials are hard to demagnetize as they don’t lose their magnetic properties easily.
What is a magnetic field?
A magnetic field is the area around the magnet where another magnet would feel a force.
What do magnetic field lines show?
Magnetic field lines show the shape and direction of a magnetic field. The magnetic field goes from the North pole to the South pole. The stronger the magnetic field, the closer the lines are together.
What happens if you try to put two like poles together? Give detail.
Like poles repel, unlike poles attract.
If you try and put two North poles (or two south poles) together, you will find it difficult as they will slide to one side. This is because they are like poles and will repel as their fields are pushing away from each other, this creates a force that pushes them apart.
By contrast, a North pole and South pole (or vice versa) will attract. The force will be an attractive force.
How can a non-metallic material become metallic?
Magnetism is induced in some materials when they are placed in a magnetic field.
Some materials that are not magnetic can become magnetic when they are in a magnetic field. This is a result of the magnetic field encouraging its electrons to align, forming north and south poles. This can happen in the four magnetic materials, nickel, iron, steel, and cobalt.
How can you track field lines?
To track field lines you can use iron filings, which are magnetic materials, they will line up along the magnetic field. You can also use compasses which will show that the lines go from north to south.
What is a solenoid?
- Magnetic field shape is similar to a bar magnet
- It enhances the magnetic effect as coiling the wire causes the field to align and form a giant single field, rather than lots of them all perpendicular to the direction of the current
- Having an iron core in the center increases its strength as it is easier for magnetic field lines to pass through than air
What are five factors that affect the strength of magnetic fields?
o Size of current o Length o Cross-sectional area o Number of turns (coils) o Using a soft iron core
