SMK (L) Methodist Kuala LumpurSTPM Physics Semester 2Definitions

Chapter 12Electrostatics1.Coulombs lawCoulombs law states that the magnitude of the electric force between two point charges is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them.

2.Electric fieldAn electric field is a region in which an electric charge experiences a force.

3.Electric field strengthThe electric field strength at a point in an electric field is the force per unit charge.

4.Electric dipoleAn electric dipole is a positive charge and a negative charge, of the same magnitude, separated by a distance.

5.Gausss lawGausss law states that the electric flux through a closed surface is given by

whereis the algebraic sum of the charges enclosed by the surface.

6.Electric potential, VThe electric potential V at a point in an electric field is the work done to bring a unit positive charge from infinity to the point.

7.Electric potential energy U of a charge qThe electric potential energy U of a charge q at a point in an electric field is defined as the work done to bring the charge q from infinity to the point.

8.Potential difference V between two points in an electric fieldThe potential difference V between two points A and B in an electric field is defined as the work done to bring a unit positive charge from one point to the other against the electric field.

Chapter 13Capacitors1.Capacitance CThe capacitance C of a capacitor is the ratio of the charge Q on either plate to the potential difference V across the capacitor.

2.Time constant

The time constant of a circuit used to discharge a capacitor is the time taken for the charge onthe capacitor to decrease to of its initial value.

The time constant of a circuit used to charge a capacitor is the time taken for the charging current to decrease to of its initial value.

Chapter 14Electric Current1.Electric current, IElectric current I is the rate of flow of electric charge.

2.Potential differenceThe potential difference V between two points in a conductor is defined as the ratio of the energy dissipated between the two points to the charge that flows.

3Resistance RThe resistance R of a conductor is the ratio of the potential difference V across the conductor to the current I in the conductor.

4.Ohms lawOhms law states that the steady current in a metallic conductor that is not a site of e.m.f. is directly proportional to the potential difference across the conductor, if physical conditions such as temperature remain constant.

5.Drift velocityThe drift velocity v is the mean velocity of the free electrons in the direction opposite to the applied electric field.

6.Current densityCurrent density, J, at cross-section in a conductor is defined as the electric current per unit area of the cross-section.

7.Resistivity The resistivity of a material is defined as the resistance of a metre length of the material that has cross-sectional area of 1 m2.

Chapter 15Direct Current Circuit1.The e.m.f. E of a sourceThe e.m.f. E of a source is defined as the energy supplied to each coulomb of charge that flows from the source.

2.Internal resistance of a dry cellInternal resistance of a dry cell is due to the resistance of the chemicals in the cell.

3.Kirchhoffs First Law

Kirchhoffs first law states that the algebraic sum of the currents entering a point in a circuit is zero.

4.Kirchhoffs Second Law

Kirchhoffs second law states that in a closed loop, the algebraic sum of the products of the current and resistance equals to the algebraic sum of the e.m.f.s in the loop.

5.MultiplierIt is a resistor connected in series with the coil of moving-coil meter so that the meter can measure a high current.

6.ShuntIt is a resistor connected in parallel with the coil of a moving-coil meter so that the meter can measure a high current.

7.PotentiometerIt is used to measure the potential difference or voltage, e.m.f. and to compare two voltages.

Chapter 16Magnetic Fields1.Magnetic fieldA magnetic field is a region where a magnetic force exists.

2.Magnetic flux density B of a magnetic field (Magnetic field strength)The magnetic flux density B of a magnetic field is the force on a charge of one coulomb (1 C) moving with a velocity of 1 m s-1 at right angles to the magnetic field.

3.Flemings Left-Hand ruleFlemings Left-Hand rule states that if the thumb, first finger and second finger of the left hand are stretched at right angles to each other, with the first finger pointing in the direction of the magnetic field B, the second finger in the direction of the velocity v of a positive charge, then the thumb points in the direction of the force F.

4.One ampereOne ampere (1 A) is the value of the steady current which, if maintained in two straight parallel conductors of infinite length and negligible circular cross-section, separated by a distance of 1 m in vacuum, would produce a force of 2 x 10-7 N m-1 on the conductors.

3.Hall EffectThe Hall effect is the phenomenon in which a transverse voltage is set up in a conductor carrying a current in a magnetic field.

Chapter 17Electromagnetic Induction1.Magnetic Flux LinkageMagnetic flux linkage is the magnetic flux linked with the coil.

2.Electromagnetic InductionElectromagnetic induction is the production of an e.m.f. in a conductor when the magnetic flux linked with the conductor changes.

3.Faradays law of electromagnetic inductionFaradays law of electromagnetic induction states that when the magnetic flux linked with a conductor changes, an e.m.f. which is directly proportional to the rate of change of magnetic flux linkage is induced in the conductor.

4.Lenzs LawLenzs law states that the direction of the induced current is such that it produces a magnetic field to oppose the change in the magnetic flux that induced the current.

5.Self InductionSelf inductance is the phenomenon in which an e.m.f. is induced in a conductor when the current in the conductor changes.

6.Back-e.m.f.An e.m.f. is induced and the resulting induced current opposes the increase in the magnetic flux. The induced e.m.f is known as the back-e.m.f.

7.Self Inductance, L

Self-inductance of a conductor, .

8.Mutual InductionMutual induction is the phenomenon in which an e.m.f. is induced in a conductor when the current in a neighbouring conductor changes.

9.Eddy CurrentsEddy currents are induced currents that flow in closed loops in a conductor.

Chapter 18Alternating Current Circuits1.Alternating currentAn alternating current (a.c.) is a current in which the direction of the current changes or reverses periodically.

2.Root-mean-square value of an a.c.The r.m.s. value of an alternating current is equal to the value of a constant direct current which can produce the same heating power as the alternating current in a given resistor.

3.Pure inductorA pure inductor has only inductance, no resistance and capacitance.

4.Reactance of an inductorReactance of an inductor is the opposition of the inductor to the flow of an a.c. and is measured in ohms.

5.Pure capacitorA pure capacitor has only capacitance, no resistance or inductance.

6.Impedance, ZImpedance Z is the vector sum of the resistance and the reactance in an a.c. circuit.

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