P4: Electric Circuits (Y11 - Spring 1) (Use Goodnotes To Remember The Circuit Symbols)

Question 1

🟠 What Sub-atomic particles make up the atom

Answer 1

Protons and neutrons make up the nucleus of an atom. Electrons move about in the space around the nucleus.

Question 2

🟠 Charges and Relative Mass of a Proton, Neutron and Electron

Answer 2

Proton:
+1 Charge
Realtive Mass of 1

Neutron:
0 Charge
Relative Mass of 1

Electron:
-1 Charge
Relative Mass of almost 0

Question 3

🟠 What is an uncharged atom (+what is a charged atom called)

Answer 3

An uncharged atom has equal numbers of electrons and protons. Only electrons can be transferred to or from an atom. A charged atom is called an ion

Question 4

🟠 What happens when you add and remove electrons from an uncharged atom

Answer 4

Adding electrons to an uncharged atom makes it negative (because the atom then has more electrons than protons)

Removing elecyrons from an uncharged atom makes it positive (because the atom has fewer electrons than protons)

Question 5

🟠 What is Charging by Friction and what are two examples

Answer 5

Some insulators become charged when you rub them with another insulator such as a dry cloth. When you rub the insulator, electrons are transferred from one of the materials to the other material.

• Rubbing a polythene rod with a dry cloth transfers electrons to the surface atoms of the rod from the cloth. So the polythene rod becomes negatively charged
• Rubbing a perspex rod with a dry cloth transfers electrons from the surface atoms of the rod on to the cloth. So the perspex rod becomes positively charged. Its positive charge is equal to the negative charge of the dry cloth.

Question 6

🟠 What forces do two charged objects exert on one another and why

Answer 6

Two charged objects exert a non-contact force on each other because of their charge. This is because a charged object (X) creates an electric fueld around itself. A second charged object (Y) in the field esperiences a force because of the field. The field, and therefore the force between the two charged objects, becomes stronger as the distance between the objects decreases.

(A Charged object creates an electric field around itself. The electric field is strongest closest to the object)

Question 7

🟠 How are objects charged by friction

Answer 7

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

• Materials that gain electrons become Negatively charged
• Materials that lose electrons are Positively charged.

Question 8

🟠 Using your knowledge of statics write a short description of how a balloon can stick to a wall.

Answer 8

Initially, the charge of the balloon is neutral, and your jumper is neutral. As you rub the balloon onto the jumper, electrons are transferred to the balloon, making it negatively charged (as it is an insulator).

The wall is neutral, and sticking the balloon onto the wall will make it stick due to the positive charges in the nucleus of atoms in the wall attracting the negative charges in the balloon. Positive and negative charges attract, therefore meaning the ballon will stay there.

Question 9

🟠 What are Static Shocks and how do they happen

Answer 9

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 10

🟠 a) Explain how the polythene rod becomes negtaively charged when it is rubbed with the cloth

b) What charge is left on the cloth. Explain your answer

Answer 10

a) The polythene rod is an insulator as well as the dry cloth. When they are rubbed together, electrons are transferred from the cloth to the rod, therefore making the rod negatively charged.
b) The charge left on the cloth is a positive charge, due to the fact that some of the electrons from the cloth have been transferred to the polythene rod, making the cloth positive as it was originaly neutral (and lost electrons)

Question 11

🟠 A plastic comb can attract pieces of paper. Explain how this can happen.

Answer 11

The comb and hair are insulators, so by combing your hair would transfer electrons to the comb, from the hair due to friction. This makes it negatively charged, therefore attracting the positively charged atoms in the nucleus in the tissue paper, as positive and negative charges attract each other.

Question 12

🟠 a) Explain how the spray-painting process makes use of static electricity

b) State the advantages of using this process to spray-paint cars.

Answer 12

a) The spray painting process makes use of static electricity, as the spray paint is positively charged as the paint loses eletcrons to the nozzle as it passes through. The positively charged paint will be attracted to the negative charge of the car door, therefore meaning that the paint stays on the door, due to the fact that positive and negative charges attract.
b) This process allows an even layer of paint as the delocalised electrons guide thenpositively charged paint to uncovered areas. This also means there us less waste, making the process quite economical.

Question 13

🟠 Do the same type of charge attract or repel

Do different types of charge attract or repel

Answer 13

• The same type of charge (i.e, like charges) and repel each other
• Different types of charge (i.e, unlike charged) and attract each other

Like charge repel. Unlike charges attract.

Question 14

🟠 What happens if two objects are oppositely charged and sparking happens

Answer 14

If the two are oppositely charged, electrons in the air molecules between the two objects experience a force towards the positive object. If the field is too strong, sparking happens, because some electrons are pulled out of air molecules by the force of the field. These electrons hit other air molecules and knock electrons out of them, creating a sudden flow of electrons between the two charged objects.

Question 15

🟠 How can you represent an electric field and how do they work?

Answer 15

You can draw lines of force to represent an electric field. When the electric field is near an isolated positively charged sphere, each line of force is the path that a small positive charge, Q, would follow because of the electric field.

The lines point away from the centre of the charged sphere because the force on Q is directed away from the sphere. If the sphere was negatively charged, the lines would point towards the centre of the sphere.

Question 16

❌ Description of a Cell

Answer 16

Provides the ‘push’ for electrons in a circuit

Question 17

❌ Description of an Ammeter

Answer 17

Used to measure current

Question 18

❌ Description of a Voltmeter

Answer 18

Used to measure potential difference (voltage)

Question 19

❌ Description of a Light

Answer 19

Emits light when current passes through it

Question 20

❌ Description of an LDR

Answer 20

Light dependent resistor

Question 21

❌ Description of a Fuse

Answer 21

Melts & breaks the circuit if the current is too high

Question 22

❌ Description of a Resistor

Answer 22

Limits the current in a circuit

Question 23

❌ Description of an LED

Answer 23

Emits light when current passes through it

Question 24

❌ Description of a Switch

Answer 24

Enables current in a circuit to be switched on or off

Question 25

❌ Description of a Thermistor

Answer 25

Temperature dependent resistor

Question 26

❌ Description of a Variable Resistor

Answer 26

Allows current in to be varied

Question 27

❌ Electric Current Definition

Answer 27

Electric current is the flow of charge.

● 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 28

❌ What is Current measured in (+ Current Definition)

Answer 28

Current is measured in amperes (‘amps’)

1 ampere is a rate of flow of 1 coulomb per second

Question 29

❌ Current Equation (Involving Time and Charge)

Answer 29

I = Q / t
Current (A) = Charge (C) / Time (s)

(t = Q/I
Q = I x t)

Question 30

❌ Current is the flow of ________ and is measured in ________ . The charged particles that flow in metals are ________ . Charge is measured in ________ . The current or charge at any point in a series circuit is always ________ . The current or charge will ________ at a junction in a parallel circuit.

(Split, Electrons, Charge, The Same, Ampere, Colomb)

Answer 30

Current is the flow of electrons and is measured in ampere . The charged particles that flow in metals are charge . Charge is measured in colomb . The current or charge at any point in a series circuit is always the same . The current or charge will split at a junction in a parallel circuit.

Question 31

❌ Example Question:

A charge of 10 C passes through a bulb in 5 seconds. Calculate the current through the bulb.

Answer 31

I = ??
Q = 10C
t = 5s

I = Q / t
= 10 / 5
= 2a

Question 32

❌ A resistor with a current of 1.2 amps for 5 seconds, calculate the charge

Answer 32

I = Q / t
Q = It

1.2 x 5 = 6.0

= 6.0 C

Question 33

❌ What is Potential Difference

Answer 33

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

Question 34

❌ Potential Difference Equation

Answer 34

V = E / Q
Potential Difference (V) = Energy (E) / Charge (Q)

E = VQ
Q = E/V

Question 35

❌ The energy transferred to a bulb is 320 J when 64C of charge passes through it. Calculate the potential difference across the bulb

Answer 35

V= ??
E = 320J 
Q= 64C

V =E / Q
= 320 / 64 = 5V

Question 36

❌ A Speaker has 30 joules of work done with a p.d of 3.0 V. Calculate the charge.

Answer 36

V = E / Q
Q = E / V

30 / 3 = 10
= 10 C

Question 37

❌ Resistance Definition

Answer 37

Electrical Resistance or Resistance in a circuit is the opposition to the flow of charge. Resistance is measured in a unit called OHMS (Ω)

Question 38

❌ What factors affect the resistance in a wire?

Answer 38

The:

• Length of wire
• Material of wire
• Temperature of material/Heat
• Tickness of wire
• Comductivity of material

Question 39

❌ What is Ohm’s Law

Answer 39

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

(The larger the resistance, the smaller the current)

Question 40

❌ Equation for Potential Difference (Involving Current and Potential Difference) (Equation Displaying Ohm’s Law)

Answer 40

V = I x R

Potential Difference (V) = Current (A) x Resistance (Ω)

Question 41

❌ Explain how current varies with voltage

Answer 41

As the current increases, the voltage also increase at exactly the same rate. They are both directly porportional.

Question 42

❌ How does the Potential Difference across a resistor relate to the current and the resistance in it and does it follow Ohm’s law

Answer 42

The potential differende across the resistor is directly proportional to the current in the resistor (V x I).

As a result:

• A resistor obeys Ohm’s law, and so can be described as ohmic conductor
• The resistance of the resistor is constant.

Question 43

❌ How does the Potential Difference across a filament lamp relate to the current and the resistance in it and does it follow Ohm’s law

Answer 43

The potential difference across a filament lamp is not directly proportional to the current through the resistor.

In other words:

• A filament lamp does not obey Ohm’s law, and so can be described as a non-phmic component
• The resistance of the filament lamp is not constant.

Question 44

❌ Why does a current-potential difference graph for a filament lamp show

Answer 44

The graph produced is not a straight line but a curved line. Increasing the voltage across the filament in the bulb causes this wire to get very hot and give out light. As the wire gets hitter, its resistance gets higher, which means the current flow is less. So as the temperature rises the current is not proportional to the volatge.

Question 45

❌ How does the Potential Difference across a diode lamp relate to the current and the resistance in it and does it follow Ohm’s law

Answer 45

• In the forward direction, the line curves towards the y-axis. So the current is not directly proportional to the potential difference. The resistance changes as the current changes. A diode is a non-ohmuc conductor.
• In the reverse direction, the current is virtually zero. So the diode’s resistande in the reverse direction is a lot higher than its resistance is in the forward direction

Question 46

❌ What is a Thermistor

Answer 46

A thermistor is a temperature-dependant resistor, and its resistance decreases if its temperature increases (and increase if the temperature decreases).

Question 47

❌ How does resistance change in an LDR

Answer 47

The resistance of a light-dependant resistor (LDR) decreases if the light intensity increase (and increases if the light intensity decreases).

Question 48

❌ What does a Resistance (Ω) (Y-axis) over Temperature (°C) (X-axis) show

Answer 48

It shows that resistance decreases in a downwards and to the right curve as temperature increases.

Question 49

❌ What does a Resistance (Ω) (Y-axis) over Light Intensity (X-axis) show

Answer 49

It shows that resistance decreases in a downwards and to the right curve as light intensity increases.

Question 50

❌ The letter I is used to represent the ………………….. flowing through a component in
a circuit. The letter V is used to represent the ………………….. across the component.
A current–potential difference (IV) graph can be used to find the …………………….. of the component. The current is plotted on the ……………. and the potential difference is plotted on the ……………. .
The circuit must contain an ammeter to measure the …………………….. and a …………………….. to measure the potential difference.

(potential difference, resistance, voltmeter, current, y-axis, x-axis)

Answer 50

The letter I is used to represent the current flowing through a component in a circuit.
The letter V is used to represent the Potential Difference across the component.
A current–potential difference (IV) graph can be used to find the Resistance of the component. The current is plotted on the y-axis and the potential difference is plotted on the x-axis.
The circuit must contain an ammeter to measure the Current and a Voltmeter to measure the potential difference.

Question 51

❌ What does a current-potential difference graph for a Dioide show and why

Answer 51

The current is not directly proportional to the potential difference. The resistance changes as the current changes, and the diode only allows current to pass through at certain values.

Question 52

❌ Explain the significance of the negative values for potential difference and current in a current-potential difference graph for a diode

Answer 52

Negative potential difference means,current can’t flow in a backwards direction, as current flows from high potential to low potential zone. Not on to the opposite direction.So if potential difference is negative, the current should flow on to the opposite direction as a result, meaning that the diode doesn’t work until a certain positive value for potential difference is met.

Question 53

❌ What is use for a Diode in a circuit

Answer 53

The use of a diode in a circuit is to allow an electrical component that allows the flow of current in only one direction. It also severely restricts current from flowing in the opposite direction.

Question 54

❌ What is use for an LED in a circuit

Answer 54

A light emitting diode (LED) is a diode that emits light when a current passes througj it in the forward direction. LEDs are used as indicators in many electronic devices such as battery chargers and alarm circuits.

Question 55

❌ What is the shape of a current–potential difference graph for a resistor

Answer 55

It is a linear graph that follows Ohm’s law, has a steady gradient, and passes through the origin.

Question 56

❌ What is the shape of a current–potential difference graph for a filament lamp

Answer 56

It’s like a cibic graph, where the line starts off going right, then curves up, passed through the origin, and then curves back off to the right.

Question 57

❌ What is the shape of a current–potential difference graph for an LED

Answer 57

The line starts off travelled straight along the x-axis at zero, passing the origin, before it eventually takes a steep turn upwards at a certain voltage.