Phys 1420 1st EditionExam # 3 Study Guide Lectures: 8-10Lecture 8 (March 10)Chapter 23 Capacitors and capacitive reactance-in an ac circuit the rms voltage Vrms across a capacitor is related to the rms current Irms.Vrms= Irms Xc. Xc is the capacitive reactance (measured in ohms). Xc= 1/2πfCThe ac current in a capacitor leads the voltage across the capacitor by a phase angle of 90° or π/2 radians. Results with the capacitor not consuming any power on average. The phasor model is useful for analyzing the voltage and current in an ac circuit. The length of the voltage phasor represents the maximum voltage V0, and the length of the current phasor represents the maximum current I0. Rotate counterclockwise in direction at a frequency f. Current phasor leads by 90° angle ahead of voltage phasor. The instantaneous values of the voltage and current are equal to the vertical components of the corresponding phasors. Inductors and inductive reactance- XL is the inductive reactance. Both voltage and current are related toinductors. The inductive reactance is measured in ohms. XL= 2πfCF is the frequency, L is the inductance. The ac current in an inductor lags behind the voltage across the inductor by a phase angle of 90° or π/2 radians. Inductors also consume no power. Also rotate counterclockwise. However since the current lags by 90°, the current phasor is behind the voltage phasor. The instantaneous values of the voltage and current are equal to the vertical components of the corresponding phasors. Circuits containing resistance, capacitance, and inductance-when a resistor, capacitor, and inductor are connected in series, the rms voltage across the combination is related to the rms current.Vrms= Irms Z. Z is the impedance of the combinationMeasured in ohms. R is the resistance, XL and Xc are inductive and capacitive reactance. Tan= XL –Xc/R. the tangent of the phase angle between current and voltage in a series RCL circuit. Only the resistor in the RCL combination consumes power. P= Irms Vrmscos .average power Resonance in electric circuits- a series RCL circuit has a resonant frequency f0 L= inductance, C is capacitance. At resonance, the impedance of the circuit has a minimum value equal to the resistance R, and the rms current has a max value. Semiconductor devices-in an n-type semiconductor, mobile negative electrons carry the current. An n-type material produced by doping a semiconductor such a silicon with a small amount of impurity atoms such as phosphorus. In a p-type semiconductor, mobile positive“holes” in the crystal structure carry the current. A p-type material is produced by doping a semiconductor with a small amount of impurity atoms such as boron. These two types of semiconductors are used in p-n junction diodes, light-emitting diodes, solar cells, and pnp and npn bipolar junction transistors. Lecture 9(March 24) Chapter 24Electromagnetic waves- consist of mutually perpendicular and oscillating electric and magnetic fields. The wave is a transverse wave, electromagnetic waves can travel through a vacuum or a material substance. All electromagnetic waves travel at speed of light (c= 3.00 x 10^8 m/s )Frequency and wavelength are related. c=fʎ. the arrangement of frequencies and wavelengths of electromagnetic waves is called the electromagnetic spectrum. Radio waves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays. Visible light = 4.0 x10^14 – 7.9 x 10^14 Hz Speed of light in a vacuum= e0 is electric permittivity, µ0 is the magnetic permeability of free space Energy carried by electromagnetic waves-the total energy density u of an electromagnetic wave is the total energy per unit volume of the wave and in a vacuum. E and B are the magnitudes of the electric and magnetic fields of the wave. The intensity of an electromagnetic wave is the power that the wave carries perpendicularly through a surface divided by the area of the surface. In a vacuum, the intensity S is related to the total energy density u. The Doppler Effect and electromagnetic waves- when electromagnetic waves and the source and observer of the waves all travel along the same line in a vacuum, the Doppler effect is given.f0 and fs are the observed and emitted wave frequencies. And vrel is the relative speed of the source and the observer. + is used when the source and the observer come together, the – is used when they move apart. Polarization- a linearly polarized electromagnetic wave is one which the oscillation of the electric field occurs only along one direction, which is taken to be the direction of polarization. The magnetic field also oscillates along only one direction, which is perpendicular to the electricfield direction. In an unpolarized wave such as the light from an incandescent bulb, the directionof polarization does not remain fixed, but fluctuates randomly in time. Polarizing materials allow only the component of the wave’s electric field along one direction to pass through them. The preferred transmission direction for the electric field is called the transmission axis of the material. When unpolarized light is incident on a piece of polarizing material, the transmitted polarized light has an average intensity that is one-half the average intensity of the incident light. When 2 pieces of polarizing material are used one after the other, the 1st is called the polarizer, and the 2nd is the analyzer. If the avg. intensity of polarized light falling on the analyzer is S0 the average intensity S of the light leaving the analyzer is given by Malus’ law. Lecture 10 (March 31) Chapter 25 Wave fronts and rays- wave fronts are surfaces on which all points of a wave are in the same phase of motion. Waves whose wave fronts are flat surfaces are known as plane waves. Rays arelines that are perpendicular to the wave fronts and point in the direction of the velocity of the wave. The reflection of light- when light reflects from a smooth surface, the reflected light obeys the law of reflection: the incident ray, the reflected ray, and the normal to the surface all lie in the same plane. And the angle of reflection equals the angle of incidence. The formation of images by a plane mirror- a virtual image is one from which all the rays of light do not actually come, but only appear to do so. A real image is one from which all the rays of light actually do emanate. A plane mirror forms an upright, virtual image that is located as far behind the