Electricity 7&8 Flashcards
Dry cell eg
Voltaic cell , Daniel cell
SI unit of electrical resistance
Ohm
What is ammeter
An instrument used to measure current in amperes
From where does current actually move in an electric cell
From negative to positive
What is voltage
Difference in electrical potential energy,per unit of charge,btw two points.
Device used to identify charge of the object
Electroscope eg gold least electroscope
BOT -
1kWh
Secondary cells are also called
Storage cells or accumulators
What is galvanometer
Used to measure small electric current.
Microwave electrical energy
1500W
Eg of secondary cells
Lead accumulators.
What do you mean by a 9 volt battery
It means that there is a potential difference of 9 volt between the 2 terminals which charges to move with a specific energy of 9 joules.
Colour of neutral wire
Black or yellow or blue
Diff btw parallel and series circuit
Parallel- same voltage
Series- share volta
What is fuse
Is a wire made of tin and lead with a porcelain holder
Colour of earth wire
Green
Dry cell example
Modified Leclanche cell was discovered by Georges Leclanche
1 kWh =
1000Wh
=3.6 x 10 raised to 6 joules in one hour
1 coulomb is equal to the
Charge of many electrons( negative energy)that is 6.25 x 10 raised to 18
Electric iron
1000W
Induction
Charging the body by bringing a charged object closely to it
Explain the working of secondary cell
There are six cells in one secondary cells. Each cell has one negative and one positive terminal . The negative cell is lead while the positive terminal is lead oxide . Each cell has a strength of 2 volts. The secondary cell contains Sulphuric acid. The vessel is made of hard rubber,glass or celluloid.
SI unit of charge
Coulomb
Electrical resistance is directly proportional to the
Temperature
How can you measure the intensity of electric current called ampere
If a charge of Q coulombs flow through a conductor in t time then intensity of electric current measured in amperes represented by I isQ/T . 1 ampere is 1 coulomb of charge flowing at a certain point at 1 second .
BOT full form
Board Of Trade unit
If there is more voltage
More current would flow
Colour of live wire
Red
What do you mean by anode and cathode
Anode is the metal to be deposited and is attached to the positive terminal. Cathode is the metal on which it has to be deposited .
SI unit of electric current
Ampere(I)
Explain process of electroplating
The copper sulphate sol, when electricity passes through it splits into cu2 + and so2-.cu2+ is attracted towards the cathode attached to the negative cell . Where electrons are given out by the electric cell.The cu2+ molecules absorb the electrons given out by the cell. They become stable molecules. After that ,the cu in the anode donates electrons to the positive terminal to create a stable ion called cu2+ Which is then attracted towards the cathode and takes electrons from the negative terminal to form a stable ion called cu. thus during this process the cu (copper)gets deposited on the cathode and the content of the anode gets eroded
Bulbs in a house are connected in …………connection
Parallel
Voltage main function
To push electrons in a circuit
Electrical energy used by air conditioner
2000 to 3000 W
Electrolyte used in simple voltaic cell
Sulphuric acid
A charged body creates an
Electric field around it
What is the relationship between an electric field and an magnetic field
A moving electric field creates a magnetic field and vice versa
According to the relationship between electric and magnetic fields what happens when a charged body moves
A charged body always has an electric field around it and as it moves a magnetic field is also created
In a proton the electric field radically points
Outwards
In an electron the electric field radically points
Inwards
Magnetic effect of electric current first discovered by
Hans Christian oersted
Electrical power is
Electrical energy / time
Instrument that measures electrical power in watts
Wattmeter
Ohms law
Voltage=rate of flow of current x resistance
P= I x V
Joules law of heating
Heat energy liberated in a circuit is
H = I*2 . R . T(time for which current is flowing)
1 Kwh = how many joules
3.6 x 10*6
All ionic compounds are
strong electrolytes, because they mostly break up into ions as they dissolve in water.
Why do ionic compounds dissociate in water
if the energy given off when the ions interact with water molecules compensates for the energy needed to break the ionic bonds in the solid and the energy required to separate the water molecules so that the ions can be inserted into solution.
Resistance of a resistor increases with its
First , Resistivity of that substance
And also length increases-more distance the electrons have to bump
Resistance of a resistor is inversely proportional to
Area-as area increases the no of electrons flowing at a point through the resistor increases
Resistance offered by a resistor formula
R = p x length/ area (p - resistivity)
A example of a rechargeable battery
Ni - fe accumulator
1 horse power (hp) = ? Watts
746 watts
A charged body creates an
Electric field around it
What is the relationship between an electric field and an magnetic field
A moving electric field creates a magnetic field and vice versa
Magnetic effect of electric current first discovered by
Hans Christian oersted
Electrical power is
Electrical energy / time
Instrument that measures electrical power in watts
Wattmeter
Ohms law
Voltage=rate of flow of current x resistance
P= I x V
Joules law of heating
Heat energy liberated in a circuit is
H = I*2 . R . time for which current is flowing
1 Kwh = how many joules
3.6 x 10*6
Why do ionic compounds dissociate in water
if the energy given off when the ions interact with water molecules compensates for the energy needed to break the ionic bonds in the solid and the energy required to separate the water molecules so that the ions can be inserted into solution.
Diamagnetic objects ?
materials that are not affected by a magnetic field.
Paramagnetic objects
materials like aluminum or platinum which become magnetized in a magnetic field but their magnetism disappears when the field is removed.
Ferromagnetic objects
materials (such as iron and nickel) that can retain their magnetic properties when the magnetic field is removed.
Charge is a
Scalar quantity
Charge cannot exist without
Mass
Quantisation of charge
It means charge cannot have any arbitrary value but is defined as a integral multiple of the basic unit such as electron
Charge of one electron
1.6 x 10 raised to -19 C
Charge of an object (q) is
ne
e - charge of proton
n - any integer
Quantisation of charge was first suggested by
Michael faraday
Quantisation of charge experimentally demonstrated by
Millikan in 1912
Conservation of charge
Charge cannot be destroyed nor created
Charge is invariant
It means charge of an object always remains same , even if it is accelerated and until charge is removed from it.
3 methods of charging
Conduction
Friction
Induction
Which type of charging is most preferred
Induction because a charged body can be used to charge Maza y other objects without losing its charge
Dielectric constant also called
Relative permittivity
Dielectric constant denoted by
K
Coulomb’s constant
K = 9 x 10 raised to 9 N m sq. C raised to -2
Principle of superposition (electricity)
It states that when a number of charges are interacting with each other , the total force on a given charge is vector sum of forces exerted on it by all other charges
Linear charge density
Charge per unit length
Linear charge density is represented by
Lambda
Surface charge density
Charge per unit area
Electric field ?
A region surrounding a charge in which its electrical effects are perceptible.
In an electric field , crowded lines represent
A stronger field
Number of lines originating or terminating on a charge is proportional to its
Magnitude
If a body has a charge of q , then no electric field lines (electrical flux) it has is
q / E°
E° - permittivity of free space
E° is the value of
Permittivity of free space
E° value?
8.854 x 10-12 C2 N-1 m-1
Electric dipole
Pair of two equal and opposite charges separated by a small distance
Point charges
Point particles with electric charge
Inside a conductor electric field is
0
3 types of capacitors
Parallel plate capacitors
Cylindrical capacitor
Spherical capacitor
Capacitor function is to
Store Charge
A capacitor consists of
2 metal strips separated by an insulating material called dielectric
Every substance has a quality called
Dielectric constant - (K)
Capacitance of a capacitor tells us
How much charge it can store
Charge stored in the metal pieces are both
Equal and opposite
Capacitors are usually charged by a battery and the voltage between the metal pieces is equal to
The voltage of battery
Capacitance formula
C = Q/V
C - capacitance
Q - charge in one of the metal pieces
V - voltage between the metal pieces
When a dielectric is introduced between 2 metal pieces in a capacitor
The molecules in it gets polarised
Due to the polarisation of dielectric in a capacitor -
Voltage decreases.
C = Q/V
So capacitance increases
If a battery is connected when the dielectric is placed between the metal pieces of the capacitor
The polarisation of dielectric reduces voltage between the metal pieces
But it is the battery’s responsibility to see that there is the same voltage in the entire circuit.
So it starts to accumulate more charge in both metal pieces to make the voltage stable,thus at this time, amount of charge in both metal pieces increases.
So according to the formula- C = Q/V - capacitance increases
Unit of capacitance
Farads (F)
How to calculate the change a dielectric will bring to the capacitance of capacitor
Every substance has something called dielectric constant (K).
So what you have to do is multiply the capacitance of the capacitor when it had no dielectric with the dielectric constant and that will be your new capacitance
pF -
Picofarad = 10*-12 farad
Capacitance is a
Scalar quantity
Insulators also called
Dielectrics
Electric constant
E° also termed as permittivity of free space.
The symbol is read as epsilon naught
……………. has lowest electrical permittivity
Vacuum
Dielectric constant (k) is
Electrical permittivity of that substance
Divided by
Electrical permittivity of vacuum
Every substance has a dielectric constant more than
1
Surface charge density represented by
Sigma
Strength of electric field
2 x Coulomb’s constant x pi x surface density
What is electrical potential energy
If a charge Q moves with a voltage V then the change in potential energy of that charge is Q times V .
Potential energy stored in a capacitor ?
1/2 x Q(charge) x voltage
In any circuit connection if you add the voltages of each of the capacitors it will be equal to
The voltage of the battery
In a series connection capacitance is added by the formula
1/C = 1/C1 + 1/C2 + 1/C3 + ………..
In a parallel connection capacitance is added by the formula
C = C1 + C2
When two capacitors with different potentials are connected to each other then
Charge moves from the higher potential to the lower potential until the potential becomes equal. This equal potential is called common potential
Common potential of two capacitors
Total charge / total capacity
In a series connection ………… is same
In parallel connection ………… is same
( for capacitors )
Charge, voltage
Capacitance of a spherical conductor of radius R
4 x pie x permittivity of free space x R
Symbol for capacitor of variable capacitor has
an arrow
Electric flux represented by the Greek symbol
Phi
Electrical flux can be found by
Multiplying strength of the electric field E with area A of a surface perpendicular to the field
To formulas for electrical flux
Flux = electrical field x area = E x A Flux = Q / E°
Q- charge enclosed
So flux = EA = Q / E°
Capacitance directly proportional to
Area
Maxwells equations contain how many equations
4
Maxwells equation?
Gauss’ law
Gauss’ law for magnetism
Ampere’s law
Faraday’s law
Gauss’ law for magnetism
This law states that magnetic monopoles do not exist
Every magnet is a dipole
Faraday’s law states that
Any change to the magnetic environment of a coil of wire , would cause a voltage to be induced on the coil
Ampere’ law states that
the magnetic field created by an electric current is proportional to the size of that electric current, with a constant of proportionality equal to the permeability of free space. .
An infinitely uniformly charged plane produces a
Constant electric field
Magnetic constant (mue 0)
4π × 10*−7 N/A2
Electric charge is a
Fundamental property
The discovery that amber rubbed by wool or silk attracted light objects was done by
Thales of Greece in 600 BC
Name electricity coined from the
Greek word - elektron meaning amber.
Property which differentiates the 2 kinds of charge
Polarisation of charge
Names were given to the 2 kinds of charge by
Benjamin Franklin
Who first observed that compass needle was deflected by a wire carrying electricity
Oersted , and supported by Michael faraday and Ampere.
Who proposed the theory which unified electric current and magnetism
Maxwell and Lorentz
An application which is connected in a circuit
Load (L)
Deflection of the needle on galvanometer shows
Presence of current and direction of deflection indicates direction of current
Ammeter is joined in
Series connection
An ammeter has a
Low resistance
In a series circuit, the current through each of the components is the same, and the voltage across the circuit is the sum of the voltages across each component. In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component.
Read
Resistance wires usually made of a compound called
Manganin
Rheostat
A device used to adjust the magnitude of current in a circuit by changing the length of resistance wire.
Symbol used for variable resistance
Rh
Voltmeter has high
Electrical resistance so that it does not draw out much current from the circuit
Manganin composition
84% copper , 12% manganese , 4% nickel
Lead accumulators also called
Acid accumulators
Ni-Fe accumulators also called
Alkali accumulators
Alternating current ?
A current whose both magnitude and direction change with time. The current repeats it’s value after a fixed time
Voltage of current reaching in homes of India
230 Volts
In an electric cell the positive electrode is called
Cathode
Potential is a
Scalar quantity
Potential SI unit is
Volt
1 horsepower = how many watts
746
Resistors in the higher range is usually made of
Carbon
How quickly an electron can flow through a conductor
Electron mobility
Drift velocity
Average speed that a particle like an electron attains in a material due to an electric field
Drift velocity =
Electron mobility x strength of electric field
1 kWh is equal to
3.6 x 10 raised to 6 joules
Internal resistance of a cell represented by a
r
Electromotive force represented by
A laterally inverted 3
Kirchhoff’s first law also called
Kirchhoff’s junction law or Kirchhoff’s current law
Kirchhoff’s first law states that
total current entering a junction is equal to the total current leaving the junction. OR The algebraic sum of currents at a junction is zero.
Kirchhoff’s second law also called
Kirchhoff’s loop law or kirchhoff’s voltage law
Meter bridge is a device used for
Measuring unknown resistance
On rubbing substances with each other , those substances which are likely to get a positive charge
Fur , wool
Glass
Hair
Nylon or acetate
On rubbing substances with each other , those substances which are likely to get a negative charge
Silk , ebonite , amber , rubber , plastic
Eg of semiconductors
Silicon , Germanium
Non electrolyte
A solution of a chemical compound which do not conduct electric current and hence do not undergo any chemical change
Eg of non electrolytes
Petrol , kerosene oil , diesel , vegetable oil , chloroform , carbon tetrachloride , alcohol , ether , benzene , distilled water
For making metals shiny it is usually electroplated with
Nickel and chromium
Coulomb was named after the French physicist
Charles Augustin de Coulomb
Triboelectric effect
a type of contact electrification on which certain materials become electrically charged after they come into frictional contact with a different material. Rubbing glass with fur, or a plastic comb through the hair, can build up triboelectricity.
Coulomb’s constant
8.987551
Electrostatic equilibrium definition
It is the position where the resultant force on a charged particle becomes 0.
Electric charge definition (IJSO book)
It is the intrinsic property of certain fundamental particles like electron, quarks etc due to which they PRODUCE magnetic and electric effects.
The charge of a macro body =
The excess or deficiency of electrons in the body.
An algebraic expression becomes a polynomial only when -
All the coefficients are real numbers.
All the powers of the variables are positive integers.
A polynomial whose coefficients are all zeros :
Zero polynomial.
Degree of a zero polynomial is
Not defined.
The real number “c” is a root of f(x) only if
f(c) = 0
Proof of remainder theorem
p(x) = q(x) (x-a) + r
Let x = a
p(a) = q(a) x 0 + r
p(a) = r
