unit 4 - electricity Flashcards
When do we get a shock?
When accumulated charges present within our body leave our body
Electrical field features, defiantion, SI unit, formula
Amount of force expirienced per unit positive charge
Region around a charged body in which its effect can be felt by other charged bodies
Vector quantity
SI unit = NC^-1
Formula = E = F/q
The direction of the electricial feidl is radially inward for negative charges and radially outward for positive charges
The field lines are always perpendicular to the surface
Coulombs law of electrostatics defination and also known as?
The electrostatic force of attraction or repulsion between 2 point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them
aka Inverse Square Law
Coulombs law final equation with constant
F = k (q_1 * q_2)/r^2
What is coulombs constant?
Represented with K
Constant:
Value in free space/air/vacuum = 9 * 10^9
Dependent on medium and changes with each medium
Properties of charges
- There are 2 types of charges (+ve and -ve)
- Like charges repel, opposites attract
- Quantization of charge
- Law of conservation of charge
What is law of conservation of charge
Charge can neither be created nor destroyed, it can only be transferred from one body to another
What is quantization of charge and formula
The net charge acting on a body is always an integral multiple of the elementary charge
Q = ± n * e
Q = net charge
n = integer/no. of electrons being transferred
e = elemntary charge
What is the elementary charge
Constant
represented with e
Least amount of charge that could be present on a stable body
Value = 1.60 * 10^-19 C
Transfer of charge through friction
Obstructs relative motion, generating heat between two bodies being rubbed, allowing the free electrons to gain enough energy to get ejected to a different body. With enough energy, the electrons can jump from one body to another allowing for flow of charge
transfer of charge through induction
The process of charging a neutral body by bringing it near another charged object, but there is no physical contact between the two
What happens to charges within a neutral body in induction
The charges get redistributed due to the influence of a charged object
Transfer of charge through conduction
The process of charging a body which involves direct physical contact between the neutral and charged objects, allowing for charge to flow between the objects
Electrons within insulators
Tightly held together with the atom and are not free to move around although they can be transferred by rubbing
Earthing
The process of electrons flowing from a charged body onto the earths ground
Potential at a point Formula and SI unit
Amount of work done per unit positive test charge in moving a small charge from infinity to that point
V = W/q
Si unit = volt
Charge will flow from where to where
From a point at higher potential to a point at lower potential by itslef
2 general statements about point charges closer to positive and negative sources
Points closer to a +ve source charge will be at a higher potential
Point closer to a -ve source charge will be at a lower potential
Current
Rate of flow of charge
Current flow is dependant on?
Potential difference, higher potential difference means a higher current
Formula for current and si unit
I = q/t
Si unit - Ampere
Ohms law and formula
For all external conditions such as temperature remaining constant, the current flowing is directly proportional to the potential difference applied across the 2 ends
V = IR
How does graph of OHms law look like
Y axis = Voltage
X axis = Current
Slope = Resistance
Conventional current flow
Flows from positive terminal (high potential) to a negative terminal (low potential). Always opposite the flow of electrons
Ohmic conductor w/ examples
Those conductors which obey ohms law like iron copper and gold
non ohmic conductors with examples
Those conductors which do not obey ohms law like tungsten
Resistance
Property of material because of which it opposes and restricts free flow of charge
Reason behind Resistance
Collisions of charged particles between free electrons and free electrons or collision with positive ions
Factors affecting resistance
Temperature, Cross-sectional area, Length of wire, material of the wire
How does cross-sectional area affect resistance?
Inversely proportional, as area increase, resistance decreases
How does length of the wire affect the resistance?
Resistance is directly proportional to length as length increases, resistance also increase. This is because electrons travel, the more collisions they will have.
What is resistivity?
Different materials offer different resistance because of a property, and that is resistivity. It converts the qualitative and uncertain data of temperature and material of resistor and converts it into measurable qualitative data
Electrical energy, defination and formula and use
Energy that is a result of movement of charged particles
Formula = VIt
V = voltage, I = current, t = time
Some appliances tores energy within the chemical store of cells and batteries such as mobile phone
Other use transform the electrical energy from the main supply into a useful form of energy
Symbol = E
Electrical power and si unit
Amount of electrical energy consumed per unit time
si unit = watt
4 equations of electrical power
P = E/t (electrical energy/time)
P = V * I (Voltage * current)
P = I^2 * R (Current^2 * resistance)
P = V^2/r (voltage^2/resistance)
1 watt electric power
If 1 joule of electrical energy is consumed by a device in 1 second, the electric power of that device is said to be 1 watt
Ideal ammeter value and why
0 ohms, since its in series with resistor, the current flowing wont be the same for ammeter and resistor and hence the ideal should be 0 ohms
Ideal voltmeter value and why
Infinite ohms, to ensure that no current can flow in the voltxmeter since its parallel with the resistor
Ammeter and voltmeter connected how? (in parallel or series)
Ammeter - Series
Voltmeter - Parallel
Current flowing in series and parallel acorss resistors
Series = Same
Parallel = Not same as multiple paths for current to travel
Potential difference in series and parallel across resistors
Series = Different
Parallel = Same and is equal to the voltage given by the power source
Potential difference (V) formula
V = W/q
Work done/charge
Charging body from neutral to -ve using conduction
Bring a negatuvely charged object in contact with a neutral object and the electrons from the negatively charged object will flow onto the neutral as the protons in the nuetral will atrract them
Changing a body from neutral to +ve using conduction
Touch a +ve charged object with the neutral object attracting its electrons. Then electrons will flow onto the rod leaving the sphere with a positive charge.
Why does a higher resistance mean a higher temperature being produced within the resistor?
Because more resistance means more collisions, and hence when the particles collide, they will release their kinetic energy in the form of heat energy to the atoms in the wire, and hence the resistance wire is heated. This is known as the heating effect of current
Best resistor (ideal for heating effect of current)
Nickel, Tungsten
RQ for coulombs law
How does changing the distance between 2 point charges affect its force of attraction/repulsion, keeping the charge present on both test charges and the medium of experiment constant throughout?
RQ for heating effect of current
How does a change in the mass of (object/specific heat capacity) affect the time it takes for it to heat from 25° to 35°, keeping the power rating of the heating element constant throughout?
RQ for series/parallel circuit
RQ: How does changing the number of resistors affect the current flowing in a series/parallel circuit for a constant voltage supplied, the resistance of the resistors, temperature, material, cross-sectional area, and length of the resistors?
How does increasing the potential difference affect the current
The strength of the electric field increases as you see an increase in the potential difference. This causes electrons to get a stronger push from the -ve terminal due to like charges repelling and the electrons will have a higher attraction to the positive terminal
Key points for Parallel circuit combinagtion
The voltage across all the resistors is the same
The net current in the circuit is equal to the sum of the individual currents
the reciprocal of the net resistance is equal to the reciprocal of the individual resistors
The net resistance is always less than any of the resistors in the combination
Key points for series circuit combination
The net voltage across the circuit is the sum of the voltage at individual resistors
The current flowing through each resistor is the same
The net resistance is the sum of the individual resistors
The net resistance is always greater than any of the resistor in the circuit
Joules law of heating
The heat energy generated by an electrical conductor is directly proportional to its resistance and square of the electric current passing through the conductor with time
Formulas for Joules law of heating + mc∆t
I^2Rt = mc∆t
V^2/R = mc∆t
VIt = mc∆t
Infinity defination with context to potential at a point
Any point beyond the electrical fiedl of the source charge
