P4 - Electrical Circuits

Question 1

What is the relative mass (Mr), charge(Q) and location(lo) of protons, neutrons and electrons?

Answer 1

Proton: (Mr)1 , (Q) +1, (Lo) nucleus
Electron: (Mr) 0 , (Q) -1 , (Lo) shells
Neutron: (Mr) 1 , (Q) 0, (Lo) nucleus

Question 2

If an atom loses electrons what happens to it and why?

Answer 2

It would become a positively charged ion, as there are more protons than electrons so there is a positive charge.

Question 3

If an atom gains electrons what happens to it and why?

Answer 3

It would become a negatively charged ion as there would be more electrons than protons so there is a negative charge.

Question 4

Explain how you charge an object, and how they get their charge.

Answer 4

You charge an object by friction, from rubbing insulating materials together. This is because electrons are transferred from one material to the other.

Materials that gain electrons become negatively charged and materials that lose electrons become positively charged.

Question 5

What type of force is the force of electrostatic attraction?

Answer 5

It is a non contact force.

Question 6

In which situation would charges attract to each other?

Answer 6

If they are oppositely charged (+-) they would attract.

Question 7

In which situation would charges repel from each other?

Answer 7

If the charges are (++ or –) and they are pushed close to one another they would repel.

Question 8

What does a positive electric field look like?

Answer 8

Lines would be going outwards.

Question 9

What does a negative electric field look like?

Answer 9

Lines would be going inwards.

Question 10

State some facts about a charged object and their electric fields.

Answer 10

A Charged object creates an electric field around itself.
The electric field is strongest closest to the object, so the closer you get the stronger the electric field becomes.

Question 11

How would a ballon stick to a wall.

Answer 11

When the ballon is rubbed on your hair it becomes negatively charged.

When it meets the wall, the positive charged in the wall are attracted causing the ballon to stick to the wall.

Question 12

Explain static shock.

Answer 12

If two oppositely charged objects are near one another, air molecules are attracted towards the positive object. If the field is really strong, sparking can occur. This is because electrons are pulled out of the air molecules. These in turn knock out other electrons, creating a sudden flow of charge between the objects

Question 13

What is an electrical current?

Answer 13

This is the flow of charge

Question 14

What does a cell do?

Answer 14

It provides the ‘push’ for electrons in a circuit.

Question 15

What does an ammeter do?

Answer 15

It is used to measure current.

Question 16

What does a voltmeter do?

Answer 16

It is used to measure the potential difference (voltage).

Question 17

What does a lamp do?

Answer 17

Emits light when current passes through it.

Question 18

What is an LDR?

Answer 18

This is a light dependant resistor.

Question 19

What does a fuse do?

Answer 19

Melts and breaks the circuit if the current is too high.

Question 20

What does a resistor do?

Answer 20

Limits the current in a circuit.

Question 21

What does an LED do?

Answer 21

It emits light when current passes through it.

Question 22

What does a switch do?

Answer 22

It enables the current to be switched on or off.

Question 23

What is a thermistor?

Answer 23

A temperature dependent resistor.

Question 24

What is a variable resistor?

Answer 24

A resistor that allows the current to he varied.

Question 25

State some facts about the electrical current.

Answer 25

- The charge is carried around the circuit by millions of electrons. - The electrons transfer energy from the power source to the components in the circuit

Question 26

What is the equation for electric current?

Answer 26

Current (A) = charge (coulombs) / time (s)

Question 27

What is potential difference?

Answer 27

P.d. is the amount of work done (energy transferred) by each coulomb of charge that passes through the circuit between two points.

Question 28

What is the formula for potential difference?

Answer 28

P.D (V) = Energy (J) / charge (Coulomb)

Question 29

What is electrical resistance?

Answer 29

Electrical resistant or resistance in a circuit is the opposition to the flow of charge. Resistance is meadured in OHMS (Omega symbol).

Question 30

What causes resistance?

Answer 30

- An increase in temperature . - Length of the wire. - The diameter or cross sectional area of the wire. - The conductivity of the material.

Question 31

What is Ohm's law?

Answer 31

The current through a resistor at constant temperature is directly proportional to the Potential difference across the resistor.

Question 32

What is the equation for Ohm's law?

Answer 32

P.D (V) = current (A) x resistance (omega symbol [ohms])

Question 33

What does 'directly proportional mean?

Answer 33

If 2 values are in direct proportion, that means that as one value increades the other vslue increases at the same rate.

Question 34

What is the method for the resistance of a wire required practical?

Answer 34

- Set up the apparatus by connecting two crocodile clips to the thin resistance wire a distance of 10 cm apart and setting the power supply to 1.5 V. - Connect the wire, using the clips, to the rest of the circuit. - Record the potential difference from the voltmeter and current from the ammeter. - Move the clips in 10 cm intervals further apart. - Take new measurements from the voltmeter and ammeter for each length reading. - Continue until the crocodile clips are a length of 1 m apart. - Calculate the resistance of each length of wire using the equation: Resistance = Voltage / Current - Then finally plot an appropriate graph such as resistance on the y axis and length on the x axis.

Question 35

What is the method for the voltage current characteristics required practical?

Answer 35

- Set up the circuit so that there is an ammeter, fixed resistor, variable resistor and voltage supply that are in series and a voltmeter that is in parallel with the fixed resistor. - Vary the voltage across the component by changing the resistance of the variable resistor, using a wide range of voltages (between 8-10 readings). Check the appropriate voltage reading on the voltmeter - For each voltage, record the value of the current from the ammeter 3 times and calculate the average current - Increase the voltage further in steps of 0.5 V and repeat steps 2 and 3 - Make sure to switch off the circuit in between readings to prevent heating of the component and wires - Reverse the terminals of the power supply and take readings for the negative voltage (and therefore negative current) - Plot a graph of average current against voltage (an I– V graph) for each component

Question 36

What does a diode look like on a current and P.D graph?

Answer 36

It looks similar to an exponential graph. Diodes do not have negative values.

Question 37

What does a filament lamp look like on a current and P.D graph?

Answer 37

The lamp begins with a steep gradient and then begins to flatten out with a shallower gradient.

Question 38

What does a resistor look like on a current and P.D graph?

Answer 38

A straight line, directly proportional - Ohmic.

Question 39

What is a series circuit?

Answer 39

A series circuit is when all the electrical components are wired one after another.

Question 40

Does the current flowing through the circuit change if more components are added in series?

Answer 40

The current that flows across each component in series is the same. If more components were added, there is more resistance so the current would decrease due to current and resistance being inversely proportional.

Question 41

Does the potential difference across the components vary from that across the voltage supply?

Answer 41

The total potential difference ( voltage) of the supply is shared between the components in series.

Question 42

How do you calculate the total resistance in series circuits?

Answer 42

The total resistance in a series circuit is the sum of the resistance of each component in the circuit. R_total = R_1 + R_2 + R_3 +.......

Question 43

What is a parallel circuit?

Answer 43

In parallel circuits components are connected in separate loops or along different 'branches'. Therefore components are placed along different paths.

Question 44

How is the current affected in parallel circuits?

Answer 44

The total current through the whole circuit is the sum of the currents through the separate branches.

Question 45

How is the voltage (potential difference) affected in a parallel circuit?

Answer 45

For components in parallel, the potential difference across each branch is the same.

Question 46

How do you calculate resistance in parallel circuits?

Answer 46

The total resistance in a parallel circuit is the sum of the resistance of each component in the circuit. 1/R_total = 1/R_1 +1/ R_2 + 1/R_3 +......