Electric Current Flashcards
What is the formula for current density,j
I/A=qnvd
What is the formula for the Cross sectional area A of a wire
πd²/4
State ohms law
It states that the current passing through a metallic conductor is directly proportional to the potential difference across it if the temperature is constant.
I¥V
Formula for resistivity
P=R A/L
Examples of ohmic conductors
Eureka wires and carbon resistors
Examples of non ohmic conductors
Thermionic diodes, junction diodes, photo cells and dilute sulphuric acid
Resistivity depends on
The material and temperature
Unit of resistivity
Ohm meter
Resistivity of ohmic materials are independent of
The magnitude E of the applied Force
20mm length wire 1.50mm in diameter has a resistance of 2.5. what is the resistance of a 35m length wire of 3mm in diameter made if the same material
1.10
What is superconductivity
This Is when some materials have a resistivity of zero below a certain temperature called critical temperature
List the applications of superconductors
They’re used in manufacturing high field superconducting magnet
Used in cables for distributing power
Used in sensitive measuring instrument and in computer technology
Positive electrode is called
Anode
What is the potential difference between the terminals of a battery
It is when no charge is allowed to flow in an external circuit known as electromotive force of the battery
When charge flows in the external circuit, the potential difference between the terminals is ________ than the emf of the battery
Lower
Unit for current
Ampere
Coulomb per second
Is current scalar or vector
Scalar
Electron flow is from ______. Terminal to ________ terminal
Negative to positive
Current in the wire is due to the flow of ________
Positive charges from positive terminal to negative terminal
Unit of qn
C/m³
_______ has the lowest resistivity
Silver
_______ is another form of ohm’s law
J=ōE
Is electric potential scalar or vector
Scalar
The energy stored by a capacitor is equal to
The work done in charging the capacitor
The work done ∆w necessary for transfer of a charge ∆q is
V∆q
Moving the plates of a capacitor closer together will_______
Increase the capacitance
What is the significance of loop rule
Conservation of energy
What is the significance of junction rule
Conservation of charge
When a glass rod is rubbed with silk what will happen
Electrons are removed from the rod
Is electric current scalar or vector
Scalar
What do you mean by varying current
A current whose magnitude changes with time
What occurs when 2 charges are moved closer together
The Force between the charges increases
Electric field strength depends on _________
Charge and distance
What is the SI unit of current density
Ampere/ meter ²
Is current density scalar or vector
Vector
What is the average velocity of Free electrons in a metal at room temperature
Zero
Three capacitors with the capacitance of C each is given a resultant capacitance of 2/3c this result can be obtained by connecting them in______
Two in series and the third in parallel across this combination
Is electric field intensity scalar or vector
Vector
The capacitor prefered for high frequency circuit is
Mica capacitor
What is used to measure the unknown emf of a cell
Potentiometer
_______is used in evaluating field intensity at a point due to a symmetric charge distribution
Gauss law
State Kirchhoff’s junction rule
It states that at any junction point, the sum of all the currents entering the junction must be equal to the sum of the currents leaving the junction
State Kirchhoff’s loop rule
This states that the algebraic sum of the potential difference around Any closed path on the circuit must be zero
Ammeter is used to measure ____?
Current
_______ is a high resistance instrument
Voltmeter
_______ has a low resistance
Ammeter
_____is an instrument which is adapted for measuring current voltage and resistance
Multi meter
