Science universe: Physics articles

Magnetism In This Chapter: ✔ Nature of Magnetism ✔ Magnetic Field ✔ Magnetic Field of a Straight Current ✔ Magnetic Field of a Current Loop ✔ Earth’s Magnetic Field ✔ Magnetic Force on a Moving Charge ✔ Magnetic Force on a Current ✔ Force Between Two Currents ✔ Ferromagnetism ✔ Magnetic Intensity Nature of Magnetism Two electric charges at rest exert forces on each other according to Coulomb’s law. When the charges are in motion, the forces are different, and it is customary to attribute the differences to magnetic forces that occur between moving charges in addition to the electric forces between them. In this interpretation, the total force on a charge Q at a certain time and place can be divided into two parts: an electric force that depends only on the value of Q and a magnetic force that depends on the velocity v of the charge as well as on Q . In reality, there is only a single interaction between charges, the electromagnetic interaction . The theory o...

Electro- magnetic Induction In This Chapter: ✔ Electromagnetic Induction ✔ Faraday’s Law ✔ Lenz’s Law ✔ The Transformer ✔ Self-Inductance ✔ Inductors in Combination ✔ Energy of a Current-Carrying Inductor Electromagnetic Induction A current is produced in a conductor whenever the cur- rent cuts across magnetic field lines, a phenomenon known as electromagnetic induction . If the motion is parallel to the field lines of force, there is no effect. Electromagnetic induction originates in the force a magnetic field exerts on a moving charge. When a wire moves across a magnetic field, the electrons it contains experience sideways forces that push them along the wire to cause a cur- rent. It is not even necessary for there to be relative motion of a wire and a source of magnetic field, since a magnetic field whose strength is changing has moving field lines associated with it and a current will be induced in a conductor that is in the path of these moving field lines. When a ...

Capacitance In This Chapter: ✔ Capacitance ✔ Parallel-Plate Capacitor ✔ Capacitors in Combination ✔ Energy of a Charged Capacitor ✔ Charging a Capacitor ✔ Discharging a Capacitor Capacitance A capacitor is a system that stores energy in the form of an electric field. In its simplest form, a capacitor consists of a pair of parallel metal plates separated by air or other insulating material. The potential difference V between the plates of a capacitor is directly proportional to the charge Q on either of them, so the ratio Q / V is always the same for a particular capacitor. This ratio is called the capacitance C of the capacitor: The unit of capacitance is the farad (F), where 1 farad = 1 coulomb/ volt. Since the farad is too large for practical purposes, the microfarad and picofarad are commonly used, where A charge of 10−6 C on each plate of 1- m F capacitor will produce a potential difference of V = Q / C = 1 V between the plates. Parallel-Plate Capacitor ...

Direct-Current Circuits In This Chapter: ✔ Resistors in Series ✔ Resistors in Parallel ✔ EMF and Internal Resistance ✔ Kirchhoff ’s Rules Resistors in Series The equivalent resistance of a set of resistors depends on the way in which they are connected as well as on their values. If the resistors are joined in series , that is, consecutively (Figure 13-1), the equivalent resistance R of the combination is the sum of the individual resistances: R = R 1 + R 2 + R 3 + L+……     series resistors Resistors in Parallel In a parallel set of resistors, the corresponding terminals of the resistors are connected (Figure 13-2). The reciprocal 1/ R of the equivalent resistance of the combination is the sum of the reciprocals of the individual resistances: If only two resistors are connected in parallel, Solved Problem 13 . 1 Find the equivalent resistance of the circuit shown in Figure 13-3( a ). Solution . Figure 13-3( b ) shows how the original...