Physics: Photoelectric Effect, de Broglie Wavelength

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Questions and Answers

Explain how the work function of a metal influences the kinetic energy of emitted photoelectrons in the photoelectric effect.

A higher work function means that more energy is required for an electron to escape the metal surface, thus reducing the kinetic energy of emitted photoelectrons, as the energy of the incident photon is fixed.

Describe how increasing the frequency of incident light affects the kinetic energy of photoelectrons, assuming the light's frequency is above the threshold frequency.

Increasing the frequency of incident light increases the energy of the photons. Since $E = hf - \phi$, increasing $f$ will increase $E$, resulting in higher kinetic energy of the emitted photoelectrons.

A photon and an electron have the same de Broglie wavelength. Which has greater total energy?

The electron has a much smaller mass than a photon's equivalent mass for the same wavelength. Therefore, the kinetic energy, and thus total energy of the electron is greater.

Explain how the de Broglie wavelength of an electron changes when its kinetic energy is quadrupled.

The de Broglie wavelength is inversely proportional to the momentum ($p = \sqrt{2mK}$). If kinetic energy ($K$) is quadrupled, momentum doubles. Therefore, the de Broglie wavelength is halved. Signup and view all the answers

A step-up transformer increases voltage from 220V to 1100V. If the primary coil has 100 turns, how many turns are in the secondary coil?

Using the transformer equation, $N_s/N_p = V_s/V_p$, we have $N_s/100 = 1100/220$. Solving for $N_s$ yields $N_s = 500$ turns. Signup and view all the answers

Explain why transformers cannot operate on direct current (DC).

Transformers rely on a changing magnetic flux to induce a voltage in the secondary coil. DC provides a constant current and thus a constant magnetic flux, so no voltage is induced in the secondary coil. Signup and view all the answers

Describe how the inductive reactance of a coil changes as the frequency of the applied alternating current increases.

Inductive reactance ($X_L = \omega L = 2\pi fL$) is directly proportional to the frequency ($f$). Therefore, as the frequency increases, the inductive reactance also increases. Signup and view all the answers

In an LCR series circuit, what condition results in minimum impedance, and what is this condition called?

Minimum impedance occurs at resonance, where the inductive reactance equals the capacitive reactance ($X_L = X_C$). This condition is called resonance. Signup and view all the answers

Describe how the different layers of the ionosphere (D, E, F1, and F2) are categorized and what primary factor influences their formation?

The layers are categorized by altitude and the primary factor influencing their formation is solar radiation, which ionizes the atmospheric gases. Signup and view all the answers

Explain why NAND and NOR gates are referred to as 'universal gates.'

NAND and NOR gates are called universal gates because they can implement any Boolean function, meaning they can be used to create any other type of logic gate (AND, OR, NOT, etc.). Signup and view all the answers

Define Zener voltage and explain why a Zener diode is typically connected in reverse bias in a circuit.

Zener voltage is the reverse bias voltage at which the diode's resistance approaches zero, leading to a sudden increase in current. Zener diodes are connected in reverse bias to operate in their breakdown region, providing a stable voltage reference. Signup and view all the answers

What is the purpose of an amplifier, and how is its effectiveness quantified using the amplification factor?

An amplifier increases the strength of a weak signal. The amplification factor quantifies this effectiveness as the ratio of output power to input power. Signup and view all the answers

Describe the key differences in construction between p-n-p and n-p-n transistors, focusing on the arrangement of the semiconductor materials.

In a p-n-p transistor, a n-type material is sandwiched between two p-type materials, whereas, in a n-p-n transistor, a p-type material is sandwiched between two n-type materials. Signup and view all the answers

Define modulation and provide two reasons why it is a necessary process in communication systems.

Modulation is the process of combining a low-frequency signal with a high-frequency carrier signal. It is necessary to reduce antenna size and avoid signal mixing from different transmitters. Signup and view all the answers

Name three basic methods of modulation and briefly describe what parameter of the carrier wave is altered in each method.

The three basic methods of modulation are Amplitude Modulation (AM), where the amplitude of the carrier wave is varied; Frequency Modulation (FM), where the frequency of the carrier wave is varied; and Phase Modulation (PM), where the phase of the carrier wave is varied. Signup and view all the answers

Explain what is meant by the 'wattless component of current' in an AC circuit and why it is considered 'wattless'.

The wattless component of current is the portion of current that does not contribute to any useful work in an AC circuit. It is considered 'wattless' because it represents energy that oscillates between the source and the load, without being dissipated. Signup and view all the answers

How does the critical angle change when light travels from water to air compared to when it travels from glass to air? Assume the refractive index of water is lower than that of glass.

The critical angle is smaller for glass to air because glass has a higher refractive index. A larger refractive index difference results in a smaller critical angle. Signup and view all the answers

Explain why total internal reflection is essential for the functioning of optical fibers used in telecommunications.

Total internal reflection ensures the light signal remains within the fiber, minimizing loss of signal strength over long distances. This allows data to be transmitted efficiently. Signup and view all the answers

A light ray is incident from air to glass at an angle of 45 degrees. If the refractive index of the glass is 1.5, find the angle of refraction inside the glass.

Using Snell's Law ($n_1\sin\theta_1 = n_2\sin\theta_2$), $. \theta_2 = \sin^{-1}(\frac{n_1 \sin\theta_1}{n_2}) = \sin^{-1}(\frac{1 \cdot \sin(45)}{1.5}) \approx 28.13$ degrees. Signup and view all the answers

Why does the color of the sunset change from yellow to orange to red as the sun approaches the horizon?

As the sun sets, sunlight travels through more of the atmosphere. Shorter wavelengths (blue, green) are scattered away, leaving longer wavelengths (yellow, orange, red) to reach our eyes. The effect is more pronounced as the sun gets closer to the horizon. Signup and view all the answers

Explain why mirages are more commonly observed on hot days, especially on roads or in deserts.

On hot days, the air near the surface is hotter and less dense than the air above. This creates a gradient in refractive index, causing light to bend upwards, creating the illusion of a reflective surface. Signup and view all the answers

Describe how the position of the observer affects the appearance of a rainbow.

A rainbow's appearance depends on the observer's position relative to the sun and the raindrops. The observer must be between the sun and the rain, with the sun behind them, to see the rainbow. Signup and view all the answers

What conditions are necessary for the formation of a primary rainbow, and how does the order of colors differ in a secondary rainbow?

For a primary rainbow, sunlight is refracted, reflected internally, and then refracted again as it exits the raindrop. The order of colors is red on the outside and violet on the inside. In a secondary rainbow, there are two internal reflections within the raindrop, reversing the color order. Signup and view all the answers

Explain how the phenomenon of total internal reflection (TIR) is utilized in endoscopes for medical imaging.

In endoscopes, optical fibers use TIR to transmit light and images from inside the body to the outside. The light is guided through the fibers due to repeated total internal reflections, allowing doctors to see internal organs without invasive surgery. Signup and view all the answers

Explain how eddy currents are utilized in an electric power meter to measure electricity consumption.

Eddy currents, induced by a rotating magnetic field, interact with the magnetic field to rotate a metal disc. The disc's rotation speed is proportional to power consumption. Signup and view all the answers

A long, straight conductor carries a steady current. How does the magnetic induction ($B$) vary with the distance ($r$) from the conductor?

The magnetic induction, $B$, is inversely proportional to the distance, $r$, from the conductor: $B = \frac{\mu_0 i}{2\pi r}$ Signup and view all the answers

A conductor of length $l$ is moving with velocity $v$ in a uniform magnetic field $B$, perpendicular to both $l$ and $v$. Explain how the magnitude of the induced EMF is derived using Faraday's Law.

The magnetic flux changes as the conductor moves, inducing an EMF. Using Faraday's Law, $EMF = -\frac{d\phi}{dt} = Blv$, where $\phi$ is the magnetic flux. Signup and view all the answers

A rectangular loop is placed in a uniform magnetic field. If the magnetic field is increased, what will happen to the current in the bar if the bar is moved?

The induced emf will be larger in magnitude, increasing the current. Signup and view all the answers

Explain how Lenz's law relates to the direction of the induced EMF in a circuit.

Lenz's law states that the induced EMF creates a current whose magnetic field opposes the change in the original magnetic field. This means the induced current 'fights' the change that caused it. Signup and view all the answers

Describe one practical application of eddy currents, other than in an electric power meter, and explain how eddy currents are used in that application.

Eddy current braking systems in trains. Eddy currents induced in the wheels create a magnetic force opposing the motion, slowing the train down. Signup and view all the answers

A copper ring and a wooden ring of the same dimensions are placed in a region of increasing magnetic field. Which ring will experience a greater induced current, and why?

The copper ring will experience a greater induced current because copper is a much better conductor than wood, allowing for easier flow of electrons. Signup and view all the answers

How does increasing the speed at which a conductor moves through a magnetic field affect the magnitude of the induced EMF?

Increasing the speed of the conductor increases the rate of change of magnetic flux, which directly increases the magnitude of the induced EMF. They are proportional. Signup and view all the answers

A string is vibrating in its fundamental mode. If the tension T and the linear mass density $\mu$ are kept constant, how does the fundamental frequency $\nu$ change with respect to the length l of the string? Express this relationship mathematically.

The fundamental frequency is inversely proportional to the length of the string. $\nu \propto \frac{1}{l}$ Signup and view all the answers

A carbon resistor is marked with the following color sequence: Yellow, Violet, Orange, and Gold. What is the resistance value and tolerance of this resistor?

Resistance is 47 kΩ, Tolerance is ±5%. Signup and view all the answers

If a stretched string has a fundamental frequency of $\nu_0$, what is the frequency of its second overtone?

$\sqrt{\frac{9}{2}}\nu_0$ or $3\nu_0$ Signup and view all the answers

A conductor of length l is moving with a velocity V in a magnetic field BE such that HE = _BE_cos$\theta$. Write down the equation for V.

$V = \frac{HE}{\mu}$ Signup and view all the answers

Two wires, one made of copper and the other of manganin, have the same length and resistance. Which wire has the larger diameter?

The manganin wire is thicker. Signup and view all the answers

A carbon resistor has the following color code: Brown, Black, Red, and Gold. Determine its resistance and tolerance.

Resistance: 1.0 kΩ, Tolerance: $\pm$5%. Signup and view all the answers

A string of length L is fixed at both ends. It vibrates in such a way that there are three antinodes formed along the string. What is the wavelength of the standing wave in terms of L?

$\lambda$ = $\frac{2L}{3}$ Signup and view all the answers

What colors represent the digits 2 and 3 in the resistor color code?

Red represents 2 and Orange represents 3. Signup and view all the answers

Describe the key difference in the output waveform between a half-wave rectifier and a full-wave rectifier when both are fed the same AC input.

A half-wave rectifier allows only one half of the AC cycle to pass, resulting in a pulsating DC with significant gaps. A full-wave rectifier inverts the negative portion of the AC cycle, using both halves to produce a more continuous pulsating DC. Signup and view all the answers

Explain how the center tap in a full-wave rectifier's transformer enables the circuit to rectify both positive and negative halves of the input AC signal.

The center tap provides two voltage sources that are 180 degrees out of phase. During the positive half-cycle, one diode is forward biased while the other is reverse biased, and vice versa during the negative half-cycle. This alternating conduction allows for rectification of both halves of the input signal. Signup and view all the answers

Why is the efficiency of a full-wave rectifier higher than that of a half-wave rectifier, assuming ideal components?

A full-wave rectifier utilizes both halves of the input AC signal, effectively doubling the power delivered to the load compared to a half-wave rectifier, which only uses one half. This leads to a higher DC output power for the same AC input, hence greater efficiency. Signup and view all the answers

Describe the function of a filter capacitor in a rectifier circuit and explain how it improves the quality of the DC output.

A filter capacitor stores charge during the peaks of the rectified waveform and releases it during the troughs. This reduces the ripple voltage, creating a smoother, more stable DC output closer to a pure DC signal. Signup and view all the answers

Explain the difference in the number of diodes required to construct a half-wave rectifier versus a bridge rectifier.

A half-wave rectifier requires only one diode, while a bridge rectifier requires four diodes. Signup and view all the answers

Create a truth table for a 2-input NOR gate.

<table> <thead> <tr> <th>Input A</th> <th>Input B</th> <th>Output</th> </tr> </thead> <tbody> <tr> <td>0</td> <td>0</td> <td>1</td> </tr> <tr> <td>0</td> <td>1</td> <td>0</td> </tr> <tr> <td>1</td> <td>0</td> <td>0</td> </tr> <tr> <td>1</td> <td>1</td> <td>0</td> </tr> </tbody> </table> Signup and view all the answers

What is the fundamental difference in the logical operation performed by an AND gate versus a NAND gate?

An AND gate outputs a HIGH signal only when all its inputs are HIGH. A NAND gate, however, outputs a LOW signal only when all its inputs are HIGH; otherwise, its output is HIGH. A NAND gate is the complement of an AND gate. Signup and view all the answers

Using only NAND gates, draw a logic circuit that performs the function of a two-input AND gate. Briefly explain how it works.

First, connect the two inputs (A and B) to a NAND gate. Then, connect the output of that NAND gate to another NAND gate with its inputs tied together. This second NAND gate acts as an inverter, effectively creating the AND function: $output = \overline{\overline{A \cdot B}} = A \cdot B $ Signup and view all the answers

Flashcards

Cathode Rays

Fast-moving electrons emitted from a cathode.

Work Function

The minimum energy needed for an electron to escape a metal surface.