Topic 1 and 2

Question 1

Describe the structure of the atom, limited to the position, mass and charge of protons, neutrons and electrons

Answer 1

An atom is made up of a positive nucleus containing positively charged protons and neutrons, which have no charge. Orbiting the nucleus are electrons which have the same size charge as a proton, but it is a negative charge, not a positive one. Protons and neutrons have the same mass, but electrons are much smaller

Question 2

Explain how an insulator can be charged by friction, through the transfer of electrons

Answer 2

When two insulators are rubbed together surface electrons are transferred from one material to another. The material that gains electrons will gain a negative charge. The material that loses electrons will be left with a positive charge.

Question 3

Explain why a material gaining electrons becomes negatively charged and a material losing electrons is left with an equal positive charge

Answer 3

Most materials have an equal number of positive and negative charges. If a material gains electrons it will have more negative charges then positive charges ? This leaves it with an overall negative charge. If a material loses electrons then it will have more positive charges than negative, and so it will have an overall positive charge.

Question 4

Describe what happens when two like, or two opposite charges are brought together

Answer 4

Two like charges repel, but two opposite charges will attract.

Question 5

Explain in terms of the movement of electrons why you can get a shock from an a car door

Answer 5

When the car drives across the floor, the rubber tyres rub against the road ? this leads to a transfer of electrons from the road to the car. When you touch the car door the excess electrons travel from the car into you ? resulting in a shock.

Question 6

Explain in terms of the movement of electrons how lightning works

Answer 6

Clouds contain ice. As the cloud moves the ice particles collide together and this results in a negative charge being built up at the bottom of the cloud (and a positive charge at the top). As this charge increases the voltage increases. Eventually there is enough voltage to create a bolt of lightning and the electrons travel in a powerful stream towards the ground.

Question 7

Explain in terms of the movement of electrons how a balloon sticks to a wall

Answer 7

When you rub a balloon it gains a negative charge. When this balloon is brought near a wall the negative charge of the balloon pushes the electrons in the surface of the wall away. This results in the front of the wall having a positive charge. The positive charge of the wall will attract the negatively charged balloon.

Question 8

Explain why a tanker is earthed, and how this can help to prevent an explosion

Answer 8

A tanker is earthed by the use of a conducting strap. The conducting strap is connected to the tanker and trails along the ground. Any electrons that the tanker gains or losses (from its tyres rubbing on the ground) will be able to travel back along the conducting strap, making the tanker neutral again. If this didn?t happen the charge would build up and could produce a spark.

Question 9

Explain some uses of electrostatic charges in everyday objects, such as paint sprayers and insecticides

Answer 9

By giving the paint sprayer a negative charge, the paint is also given a negative charge. When the paint is sprayed because it is all negatively charged the paint droplets repel and this produces a fine mist. The object being sprayed is given the opposite charge and so the paint is attracted to the car ? this can even allow it to bend around corners ? and reach those hard to get to areas.

Question 10

Explain some of the dangers of electrostatics

Answer 10

When a build up of charge occurs it can cause shocks, and produce sparks which can be dangerous when near anything flammable (like petrol).

Question 11

Define ?electric current?

Answer 11

Electric current (symbol ?I?) is the rate of flow of electrons around a circuit, and is measured in Amps (A)

Question 12

What carries the electrical current through a metal wire?

Answer 12

Electrons carry electric current through a wire.

Question 13

Which type of current is supplied by a cell or battery?

Answer 13

A cell or battery supplies direct current.

Question 14

What is the difference between A.C. and D.C.

Answer 14

A.C. stands for alternating current. This is an electric current which travels both directions around a circuit (It does not go both directions at the same time, but alternates between clockwise and anticlockwise). D.C. stands for direct current and only travels one way around the circuit.

Question 15

What does an ammeter measure, and how must it be connected in a circuit.

Answer 15

An ammeter measures the current in a circuit and must be connected in series.

Question 16

What happens to current at a junction

Answer 16

At a junction the current splits, some of it going in each direction.

Question 17

Explain how the current in a circuit depends on the voltage and resistance in the circuit

Answer 17

The equation I=V/R shows that when you double the voltage ? the current doubles. When you double the resistance the current halves.

Question 18

What does a voltmeter measure and how must it be connected in a circuit

Answer 18

A voltmeter measures the voltage across a component and must be placed in parallel

Question 19

Define potential difference/voltage

Answer 19

The potential difference (voltage) is the energy transferred per unit of charge. It is measured in volts or joules per coulomb.

Question 20

Explain how a variable resistor effects the current in the circuit

Answer 20

When a variable resistor is used to increase the resistance the current decreases. When it is used to decrease the resistance the current increases.

Question 21

How does current vary with voltage in a filament lamp?

Answer 21

At higher voltages the bulb will be hotter. This increases the bulbs resistance. If you double the voltage, the current still increases, but it does not double because of the increase in resistance.

Question 22

How does current vary with voltage in a Diode?

Answer 22

As you increase the voltage the current increases. For low voltages the current increases slowly, but for high voltages it increases much more quickly. For negative voltages (this is the same thing as turning the battery around so it?s the other way) no current will flow.

Question 23

How does current vary with voltage in a fixed resistor?

Answer 23

The current increases linearly. If you double the voltage you double the current.

Question 24

How does the resistance of a light-dependent resistor (LDR) change with light intensity

Answer 24

When the light intensity is higher (the light is brighter) the resistance drops, so more current flows. The opposite happens when the light intensity decreases.

Question 25

How does the resistance of a thermistor change with changing temperature

Answer 25

When the temperature is higher (the light is brighter) the resistance drops, so more current flows. The opposite happens when the temperature decreases.

Question 26

Explain why when there is an electrical current in a resistor, there is an energy transfer which heats the resistor ? explain in terms of electrons and ions.

Answer 26

Conducting wires are made of ions, with a ?sea? of electrons moving between them. When you pass a current through the wire the electrons move through the wire in one direction. On their way around the circuit the electrons collide with the ions, and these collisions produce heat.

Question 27

Distinguish between the advantages and disadvantages of the heating effect of an electric current.

Answer 27

In most circuits the heating effect in a circuit is a disadvantage as it means energy is lost to the surroundings. This means that appliances are less efficient and therefore cost more to run. The advantages of this heating effect is that it can be used in kettles or hairdryers for useful purposes.