Block4: Electricity and Magnetism

Question 1

What are the poles of a magnet?

Answer 1

The point that the magnet has its strongest effect

Magnets have a north and a south pole which makes them dipoles

Question 2

What kind of forces do magnets exert on each other?

Answer 2

attractive and repulsive forces

unlike poles attract each other and like poles repel each other

Question 3

What is the difference between soft and hard magnets?

Answer 3

Soft magnets are easy to magnetize but they loose their magnetism quickly while hard magnets take long to magnetize but keep their magnetism much longer.

Question 4

What are some methods of magnetism?

Answer 4

1. a piece of material can become magnetized if it is stroked consistently in one direction for a certain time period
2. another way is to create a electromagnet which means that you will wrap a wire around a nail and supply electricity through it to create a magnetic effect

Question 5

How do you increase the strength of an electromagnet?

Answer 5

increase the current flowing through it.
increase the number of turns in the wire on the coil
add a soft iron core

Question 6

What is a solenoid?

Answer 6

The elongated coil of many turns.

Question 7

What are some methods of demagnetization?

Answer 7

1. Hammer the magnet.
2. If you place a magnet in a field of an electromagnet that is connected to an alternating current it will loose its magnetism.
3. Heating a magnet will also cause it to loose its magnetism.

Question 8

What is the biggest difference between an electromagnet and permanent magnets?

Answer 8

Permanent magnets stay magnetized for a long time while electromagnets loose and gain magnetism very fast when a current is switched on and off.

Question 9

What are the two types of static electricity referred to as?

Answer 9

Positive charge and negative charge.

Question 10

What can we say about the forces that electric charges exert on each other?

Answer 10

Like charges repel and unlike charges attract each other.

Question 11

What unit is charge measured in?

Answer 11

measured in coulomb (C)

Question 12

How can objects become electrically charged?

Answer 12

If objects gain or loose an electron they can become positively or negatively charged (called an ion)

*the object never loses electrons but just transfers them between objects.

Question 13

How do you charge an object by friction?

Answer 13

The friction of two objects being rubbed together transfers electrons between the objects.
If an object gains electrons it becomes negatively charged and if an object loses electrons it becomes negatively charged.

Question 14

What is polarization?

Answer 14

When a charged object has an effect on a neutral object nearby that it makes one end of the object more positive and the other end more negative.

Question 15

How do you charge a metallic conductor by conduction?

Answer 15

When two objects come into contact with each other and one has excess electrons the objects will try to find electrostatic equilibrium to make the objects neutral.

Question 16

What does it mean to charge metallic conductors by induction?

Answer 16

A charged object (for example with a negative charge) near a conductor causes the electrons to be pushed back (one side positive and the other negative) , then if the object is grounded the electrons move off and the object now has a positive charge.

Question 17

What is an electric field?

Answer 17

The region in which an electric charge experiences a force.

Question 18

What is the difference between a conductor and an insulator?

Answer 18

A conductor has mobile charged particles(called free electrons) and can conduct and an insulator doesn’t have mobile charged particles and can’t conduct.

Question 19

How do you measure current?

Answer 19

Using an ammeter that mustn’t disrupt the flow of charge.

Question 20

What is an electric current?

Answer 20

The rate of flow of electric charge.

I=Q/change in t

Question 21

Why do we need potential difference?

Answer 21

Because without a potential difference particles have no where to flow naturally but with potential difference they flow easily from positive to negative.

Question 22

What is the emf of a battery?

Answer 22

The work done by a battery to move a unit of charge from the low to high potential terminal

Question 23

What is electrical resistance?

Answer 23

the tendency of a conductor to oppose the flow of charge.

R= V/I

Question 24

What are the factors that affect resistance?

Answer 24

temperature- thermal vibrations increase with temp and therefore resistance
length of conductor- longer wire= more collisions = more resistance
cross-sectional area of conductor- bigger area for electrons to pass through per minute= bigger current = less resistance

Question 25

ohms law:

Answer 25

I= V/R

means current is a consequence of potential difference

Question 26

Power formula:

Answer 26

power= energy transferred/ time taken
P=E/t
or P=IV

Question 27

Energy transformed formula:

Answer 27

E= IVt

Question 28

What is a resistor?

Answer 28

An electrical component that is used to control the amount of current flowing around a circuit

Question 29

What is a variable resistor?

Answer 29

can be used to alter the current that is flowing in a circuit

Question 30

What is a transducer?

Answer 30

any device whose electrical properties change when its environment changes

Question 31

What is a light-dependent resistor (LDR)?

Answer 31

It is a type of resistor whose resistance depend on the amount of light falling on it.

Question 32

What is a thermistor?

Answer 32

It’s a resistor whose resistance depends on its environment.
The resistance changes by a large amount over a narrow range of temperatures.

Question 33

How does a relay work?

Answer 33

It’s a type of switch that works using an electromagnet, then making two complete circuits.

Question 34

What is a diode?

Answer 34

a diode is a component that allows electric flow in one direction only.
(the direction of the conventional current is shown with an arrow)

Question 35

How does a logic gate work?

Answer 35

Its a device that receives one or more electrical input signals and produces an output signal that depends on those input signals.

Question 36

For resistors in series:

Answer 36

The combined resistance is equal to the sum of the resistors. R=R1+R2+Rn
The current is the same at all points around the circuit.
Voltage: V=V1+V2+Vn

Question 37

For resistors in parallel:

Answer 37

The effective resistance is less that the resistance of either resistor. 1/R=1/R1+1/R2+1/Rn
The current from the source is greater than the current through either resistor. I=I1+I2+In

Question 38

What are some electrical safety devices?

Answer 38

fuses

circuit breakers

Question 39

What are some uses of electromagnets?

Answer 39

used in scrap-yards for sorting, generators, motors, loudspeakers, computer disc drives, electric bells, buzzers and telephones.

Question 40

Why are electromagnets used so widely?

Answer 40

Because they can gain and loose magnetism very quickly.

Question 41

What is the motor effect?

Answer 41

It’s a current-carrying wire in the presence of a magnetic field and it experiences a force.

Question 42

What is Fleming’s left hand rule?

Answer 42

A way to find the direction of a force on a wire.
thumb= force
index finger= magnetic field
middle finger= current

Question 43

How do we increase the force on a wire?

Answer 43

• increase the current
• increase the magnetic field strength
• make sure that the current is perpendicular to the magnetic field lines

Question 44

How are beams of charged particles deflected in magnetic fields?

Answer 44

using a slip ring commuter which then keeps the coil in a continuous rotation.