1
Q
Define a radial field.
A
A field where the force is directed towards the center of a mass
The strength of a radial field decreases with distance from the massive body.
2
Q
Define a uniform field.
A
A field where the gravitational field strength is constant throughout
This is typically observed over small distances compared to the Earth’s radius.
3
Q
What is the unit of gravitational field strength?
A
Newton per kilogram (N kg⁻¹)
For example, the gravitational field strength at the surface of the Earth is approximately 9.8 N kg⁻¹.
4
Q
What does the weight of an object represent?
A
The force of gravity acting on it
Weight is calculated as F = mg, where g is the gravitational field strength.
5
Q
What is the acceleration of a freely falling object described as?
A
g
This indicates that the object accelerates downwards due to gravity.
6
Q
What happens to the gravitational field strength as distance from the Earth increases?
A
It decreases
The gravitational field strength is radial and varies with distance from the massive body.
7
Q
What is the relationship between gravitational field strength and distance in a radial field?
A
Strength decreases with increasing distance from the massive body
This is due to the inverse square law of gravitation.
8
Q
Define gravitational potential.
A
Work done per unit mass
Gravitational potential is defined in terms of the work done to move a small object from infinity to a point in a gravitational field.
9
Q
What is the formula for the change in gravitational potential energy (gpe) when moving from gravitational potential V1 to V2?
A
Ep = m(V2 - V1) = mΔV
This formula shows the relationship between mass and the change in gravitational potential.
10
Q
Where must an object be placed for its gravitational potential energy to be zero?
A
At infinity
The gravitational potential is defined as zero at an infinite distance from the mass creating the gravitational field.
11
Q
The unit of gravitational potential is __________.
A
J kg-1
This unit represents joules per kilogram, indicating energy per unit mass.
12
Q
True or false: The gravitational potential at a point is the work done per unit mass to move an object from that point to infinity.
A
FALSE
It is the work done per unit mass to move an object from infinity to that point.
13
Q
What is the potential gradient at a point in a gravitational field?
A
Change of potential per meter
The potential gradient indicates how gravitational potential changes with height.
14
Q
The gravitational field strength g is the negative of the __________.
A
Potential gradient
This relationship shows that gravitational field strength acts in the opposite direction to the potential gradient.
15
Q
For small changes in height compared to the Earth’s radius, which formula can be applied?
A
ΔEp = mgΔh
This formula estimates potential energy changes for small height differences.
16
Q
What does Newton’s law of gravitation state?
A
Any two masses exert a force on each other
This law describes how gravitational attraction varies with distance.
17
Q
Can spherical objects like planets be treated as point masses?
A
Yes
Newton assumed planets and the Sun were point masses to explain gravitational attraction.
18
Q
What is Kepler’s third law?
A
The square of the time period of a planet’s orbit is proportional to the cube of the average radius of its orbit
This law relates the orbital period and distance of planets from the Sun.
19
Q
What does Newton’s law of gravitation assume about the gravitational force between two point objects?
A
- Always an attractive force
- Proportional to the mass of each object
- Proportional to 1/r², where r is their distance apart
These assumptions are fundamental to understanding gravitational interactions.
20
Q
The equation for gravitational force is summarized as F = Gm₁m₂/r². What does G represent?
A
The universal constant of gravitation
G is a constant that quantifies the strength of the gravitational force between two masses.
21
Q
What are the units of the universal constant of gravitation (G)?
A
Nm²/kg²
This unit can be derived from the gravitational force equation.
22
Q
What is the value of G?
A
6.67 × 10⁻¹¹ N m² kg⁻²
This value is crucial for calculating gravitational forces in physics.
23
Q
What is the formula for gravitational field strength at a distance r from a point mass?
A
g = GM / r²
This formula is derived from Newton’s law of gravitation.
24
Q
What does the graph of g against r for points outside the surface of a planet look like?
A
Inverse-square law curve
The graph shows that g decreases in inverse proportion to r².
25
What is the **gravitational potential** at distance r from the centre of a planet?
V = - GM/r
## Footnote
This equation describes the gravitational potential due to a spherical mass.
26
The **escape velocity** (Vesc) from a planet is given by which formula?
Vesc = √(2GM/R)
## Footnote
This formula derives from the condition that the initial kinetic energy must equal the work done against gravitational potential.
27
What is the **condition needed** for a satellite to be in a stable orbit?
The centripetal force must equal the gravitational force
## Footnote
This ensures that the satellite remains in a consistent path around the Earth.
28
What happens to the **speed of a satellite** if it moves closer to the Earth?
The speed increases
## Footnote
This is due to the stronger gravitational pull experienced at lower altitudes.
29
Why must a **geostationary satellite** be in an orbit above the Equator?
To match the Earth's rotation
## Footnote
This allows the satellite to remain fixed over a specific point on the Earth's surface.
30
According to **Kepler's third law**, what does the time period of a planet orbiting the sun depend on?
The mean radius of the orbit
## Footnote
This relationship is expressed as T² ∝ r³.
31
What does **F ∞ 1/r²** represent in Newton's gravitational theory?
The force of attraction varies with distance
## Footnote
This is known as the inverse-square law.
32
What are the **two types of satellites** mentioned?
* Natural satellites (e.g., the Moon)
* Artificial satellites
## Footnote
Natural satellites orbit planets, while artificial satellites are human-made.
33
What is the **gravitational force** formula?
F = GMm/r²
## Footnote
Where G is the gravitational constant, M is the mass of one object, m is the mass of the other, and r is the distance between their centers.
34
What is a **geostationary satellite**?
A satellite that orbits directly above the equator with a time period of exactly 24 hours
## Footnote
It remains in a fixed position above the equator due to matching the Earth's rotation.
35
True or false: A **geosynchronous orbit** is the same as a geostationary orbit.
FALSE
## Footnote
A geosynchronous orbit is a 24-hour orbit that is inclined to the equator.
36
What is the process to **charge a metal object**?
* Isolate the metal from the ground
* Transfer electrons to or from the metal
## Footnote
Electrical conductors contain free electrons that can be moved to change the charge.
37
What does the **direction of an electric field line** indicate concerning a test charge?
The direction indicates the direction of the force on a positive test charge
## Footnote
Electric field lines point away from positive charges and towards negative charges.
38
How can the **strength of an electric field** be illustrated?
By using field lines
## Footnote
The density of the field lines represents the strength of the electric field.
39
True or false: **Like charges repel** and **unlike charges attract**.
TRUE
## Footnote
This fundamental principle governs electrostatic interactions.
40
What happens to an **uncharged atom** when it gains electrons?
It becomes negatively charged
## Footnote
An uncharged atom has an equal number of protons and electrons.
41
Fill in the blank: **Electrical conductors** contain lots of ______.
free electrons
## Footnote
These electrons are not attached to any one atom and can move freely.
42
What occurs when a charged conductor is **earthed**?
Electrons transfer from the Earth to neutralize or discharge the conductor
## Footnote
This process helps to eliminate excess charge.
43
What distinguishes **electrically insulating materials** from conductors?
Insulators do not contain free electrons
## Footnote
All electrons in insulators are attached to individual atoms.
44
Fill in the blank: **Antistatic materials** allow charge to flow across the ______.
surface
## Footnote
This helps to prevent the buildup of static electricity.
45
What happens to an **earthed conductor** when it comes into contact with a charged **battery**?
It will become charged
## Footnote
An earthed conductor can acquire charge from a nearby charged battery.
46
What do oppositely charged objects create in terms of **field lines**?
A concentrated field at the points
## Footnote
The field lines become denser at the points where the charges are located.
47
In the case of a point object near an oppositely charged **flat plate**, how are the field lines oriented?
At right angles to the plate where they meet
## Footnote
The field lines are concentrated at the point object.
48
What is the characteristic of the electric field between two **oppositely charged plates**?
The field lines run parallel to each other
## Footnote
This indicates a uniform electric field between the plates.
49
The strength of the electric field is strongest where the field lines are _______.
most concentrated
## Footnote
This concentration indicates the intensity of the electric field.
50
What experimental setup is used to visualize electric field patterns using **semolina grains**?
Connecting two metal conductors to a high-voltage supply unit
## Footnote
The grains align along the field lines, similar to compasses in a magnetic field.
51
What is the unit of **electric field strength (E)**?
newton per coulomb (NC-1)
## Footnote
This unit measures the force experienced by a charge in an electric field.
52
Is **electric field strength (E)** a scalar or a vector?
vector
## Footnote
Electric field strength is a vector in the same direction as the force on a positive test charge.
53
Why should **E** be described as the force per unit charge instead of the force that acts on one coulomb of charge?
Because a test charge must be very much less than one coulomb
## Footnote
A larger charge would affect the charges causing the field, altering the electric field strength.
54
What is the equation for the force **F** on a test charge **Q** in an electric field with strength **E**?
F = QE
## Footnote
This equation relates the force experienced by a charge to the electric field strength.
55
What is the direction of the force on an **electron** in an electric field directed downwards?
upwards
## Footnote
The force on an electron is opposite to the direction of the electric field due to its negative charge.
56
What is the equation to calculate electric field strength **E** from the potential difference **V** and separation **d** between two plates?
E = V/d
## Footnote
This equation shows the relationship between electric field strength, potential difference, and distance.
57
What is **gravitational potential**?
The potential energy per unit mass at a point in a gravitational field
## Footnote
It is defined as the work done to bring a mass from infinity to that point.
58
What does an **electric field** exist near?
A charged body
## Footnote
The strength of the electric field is greater with a higher charge on the body.
59
The electric field strength between charged parallel plates is proportional to what?
Charge per unit area on the facing surfaces
## Footnote
This relationship is crucial for understanding electric fields in capacitors.
60
What is the value of **epsilon nought** (ε₀)?
8.85 x 10^-12 farads per metre (Fm^-1)
## Footnote
It is the permittivity of free space, representing charge per unit area that produces an electric field strength of one volt per metre.
61
What is **electric potential** defined in terms of?
The work done per unit positive charge
## Footnote
Electric potential is a measure of the potential energy per unit charge at a point in an electric field.
62
How do you calculate the **electric potential difference** between two points?
By finding the work done on a test charge moving between the two points
## Footnote
The potential difference is the difference in electric potential energy per unit charge.
63
What is the unit of **electric potential**?
Volt (V)
## Footnote
1 Volt is equal to 1 Joule per Coulomb (1 V = 1 J/C).
64
The electric potential at a position is given by the formula **Ep = QV**. What do the variables represent?
* Ep: Electric potential energy
* Q: Charge
* V: Electric potential
## Footnote
This formula relates electric potential energy to charge and electric potential.
65
True or false: Moving a test charge from a position of higher potential to lower potential requires work to be done on the charge.
FALSE
## Footnote
Work is done by the electric field on the charge when moving from higher to lower potential.
66
What does the **potential gradient** represent in an electric field?
The potential per unit change of distance in a given direction
## Footnote
It indicates how quickly the electric potential changes with distance.
67
Fill in the blank: The electric field strength E is equal to the negative of the _______.
potential gradient
## Footnote
This relationship shows how electric field strength relates to changes in electric potential.
68
Who first established the link between **charged objects** and their forces?
Charles Coulomb
## Footnote
He established this link in France in 1731.
69
What happens when a charged ball on a rod is placed in contact with another ball on the needle?
The second ball is charged
## Footnote
This causes it to be repelled by the first ball.
70
What does the **twist** in the wire of Coulomb's torsion balance indicate?
The electrical repulsion force
## Footnote
The twist balances the repulsion force between the balls.
71
What is the relationship between the **force** and the **distance** between two point charges according to Coulomb's law?
Force is proportional to 1/distance²
## Footnote
This means that as the distance decreases, the force increases significantly.
72
What does the **sign** of the force (+ or -) indicate in Coulomb's law?
The nature of the interaction
## Footnote
A positive sign indicates repulsion, while a negative sign indicates attraction.
73
What is the formula for the **force F** between two point charges Q1 and Q2?
F = k * (Q1 * Q2) / r²
## Footnote
Here, r is the distance between the charges and k is Coulomb's constant.
74
Similarities between Gravitational Fields and Electrostatic Fields
75
Differences between Gravitational and Electrostatic Fields
76
What is the **definition of capacitance**?
The charge stored per unit potential difference (pd)
## Footnote
The unit of capacitance is the farad (F), equal to one coulomb per volt.
77
What is the **equation** for capacitance?
C = Q / V
## Footnote
Rearranging gives Q = CV or V = Q / C.
78
List the **uses of capacitors**.
* Smoothing circuits
* Back-up power supplies
* Timing circuits
* Pulse-producing circuits
* Tuning circuits
* Filter circuits
## Footnote
Capacitors are essential in various electronic applications.
79
What happens to the **charge on a capacitor** when it charges up?
The plate gains an equal and opposite charge
## Footnote
This is fundamental to how capacitors store energy.
80
What is the relationship between **current (I)**, **time (t)**, and **charge (Q)** in a capacitor?
Q = It
## Footnote
This equation shows how charge is accumulated over time with a constant current.
81
What is the **potential difference (pd)** across a capacitor when it stores charge?
It varies with time during charging
## Footnote
The pd can be measured using a high-resistance voltmeter connected in parallel.
82
What is the **definition of capacitance**?
The charge stored per unit potential difference (pd)
## Footnote
The unit of capacitance is the farad (F), equal to one coulomb per volt.
83
What is the **equation** for capacitance?
C = Q / V
## Footnote
Rearranging gives Q = CV or V = Q / C.
84
List the **uses of capacitors**.
* Smoothing circuits
* Back-up power supplies
* Timing circuits
* Pulse-producing circuits
* Tuning circuits
* Filter circuits
## Footnote
Capacitors are essential in various electronic applications.
85
What happens to the **charge on a capacitor** when it charges up?
The plate gains an equal and opposite charge
## Footnote
This is fundamental to how capacitors store energy.
86
What is the relationship between **current (I)**, **time (t)**, and **charge (Q)** in a capacitor?
Q = It
## Footnote
This equation shows how charge is accumulated over time with a constant current.
87
What is the **potential difference (pd)** across a capacitor when it stores charge?
It varies with time during charging
## Footnote
The pd can be measured using a high-resistance voltmeter connected in parallel.
88
What does a **capacitor** store as it is being charged?
Energy
## Footnote
A capacitor stores energy in the form of an electric field created by the separation of charges.
89
The total energy stored in a capacitor can be represented by the equation **E = 1/2 CV^2**. What do the variables stand for?
* E: Energy stored
* C: Capacitance
* V: Voltage
## Footnote
This equation shows the relationship between energy, capacitance, and voltage.
90
What device can measure the **energy transfer** from a charged capacitor to a light bulb during discharge?
Joulemeter
## Footnote
The joulemeter records the energy before and after discharge to determine the energy transferred.
91
In the charging process, the battery forces charge **Q** through the circuit, transferring energy **QY** to the circuit. What does **Y** represent?
Voltage
## Footnote
This indicates the energy transferred per unit charge.
92
What is the relationship between the **work done** and the energy stored in a capacitor?
The total energy stored is represented by the area under the charge-voltage graph
## Footnote
This area corresponds to the work done in charging the capacitor.
93
What happens to the energy stored in a capacitor when it discharges?
It is transferred to the circuit
## Footnote
The energy stored is released during the discharge process, powering devices like light bulbs.
94
What is the **time constant** of a capacitor-resistor circuit?
RC
## Footnote
The time constant is a measure of the time it takes for the charge or voltage to decrease to approximately 37% of its initial value.
95
Describe the shape of the **charging curves** and the **discharging curves** of a capacitor.
* Charging curves: Exponential increase
* Discharging curves: Exponential decrease
## Footnote
The charging curve approaches the maximum voltage asymptotically, while the discharging curve approaches zero asymptotically.
96
To make the charge/discharge of a capacitor **slower**, which circuit components would you change?
* Increase resistance
* Increase capacitance
## Footnote
Changing these components affects the time constant, thus altering the rate of charge and discharge.
97
True or false: The charge on a capacitor will eventually reach zero.
TRUE
## Footnote
Theoretically, the charge approaches zero but never actually reaches it due to the nature of exponential decay.
98
What is the **inverse function** of e?
Inx
## Footnote
This is used to calculate time when given other parameters in the discharge equation.
99
What is the effect of a **dielectric** on a capacitor?
Increases the charge stored for a given pd across the capacitor terminals
## Footnote
The effect of a dielectric is to increase the capacitance of the capacitor.
100
Define **relative permittivity**.
The ratio of charge stored with a dielectric to charge stored without it
## Footnote
Relative permittivity, e, is defined as e = Q/Q0, where Q is the charge stored with the dielectric and Q0 is the charge stored without.
101
Describe the action of a **simple polar molecule** in an electric field.
* Electrons are pulled towards the positive plate
* The positive side of the molecule faces the negative plate
* The molecule aligns with the electric field
## Footnote
Polar molecules rotate in response to the electric field, leading to charge separation.
102
What happens to the **charge** on the plates of a capacitor when a dielectric is inserted?
* Positive side attracts more electrons from the battery
* Negative side pushes electrons back to the battery
## Footnote
This results in more charge being stored on the plates.
103
The capacitance of a capacitor is increased by which of the following factors?
* Increasing the area A of the plates
* Decreasing the spacing d between the plates
* Using a dielectric with a large relative permittivity
## Footnote
These factors contribute to achieving a larger capacitance.
104
Fill in the blank: The **relative permittivity** is defined by the equation e = _______.
Q/Q0
## Footnote
Where Q is the charge stored with the dielectric and Q0 is the charge stored without.
105
True or false: Inserting a dielectric into a capacitor decreases the capacitance.
FALSE
## Footnote
The insertion of a dielectric increases the capacitance of the capacitor.
106
What are examples of **dielectrics** mentioned in the text?
* Polythene
* Waxed paper
## Footnote
These materials are used to increase the capacitance in capacitors.
