Unit 13 Lab - Trisha Menon

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University of Illinois, Urbana Champaign *

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Physics

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Apr 3, 2024

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PHY-222 Classical Physics II (online) Radio Waves & Electromagnetic Fields SIM Homework 1) For this question, use the Radio Waves & Electromagnetic Fields simulation to guide your understanding of how Radio broadcasting and Radio receivers work. a) How is the radiating electric field (or electromagnetic signal) produced when radio stations broadcast? Include a description of what is producing the signal as well as the reasoning behind how this could produce a signal. The electromagnetic radiation is created from the accelerating charges. I could see the electrons in the radio transmitter oscillating and accelerating. This forces the electrons to change their directions because of the oscillation. b) How does your antenna work to detect this electromagnetic signal produced when radio stations broadcast? Include the physics principles that support your description of how this signal is detected. Electromagnetic radiation is a type of energy that constantly exerts an oscillating force on the electrons. The force is exerted in only one direction, but changes this direction to the opposite to produce a rhythmic and cyclical process. The radio waves pass by in the antenna, pushing on the electrons in the antenna and finally making the electrons oscillate for the length of the antenna and produce currents. Therefore, the antenna detected the electromagnetic signals. 2) Using the simulation, adjust the transmitter so that it is in sinusoidal mode and the electrons are oscillating up and down at a regular frequency. This is how radio waves are broadcast. Set it so that both “display the curve” and the “radiated field” boxes are checked. a) What does the curve represent? (Select the correct statement below) i) The line of electrons being sprayed off of the antenna that then cause the receiver electron to move. ii) The path that an electron will follow due to the electromagnetic wave. iii) The evenly spaced electrons moving up and down between the two antennae. The field of negative charges that are moving through space. iv) The strength and direction of the force that would be exerted by the electromagnetic wave on an electron. Correct statement is: _____ iv _____

PHY-222 Classical Physics II (online) b) With the frequency set at the mid-point of the slider and the amplitude set at the mid-point of the slider, approximately how many grid marks is the wavelength of the wave (use the pause button and step button as you need to in order to get a good measure, and round to the nearest whole grid mark)? The wavelength of the transmitter is about 5 grid marks. If the amplitude is increased, the wavelength (Select the correct statement below) i) Decreases ii) Increases iii) Stays the same Correct statement is: ____ iii ______ c) Use the simulation to evaluate the following True/False statements. i) If the oscillation frequency of the transmitting electron decreases, the oscillation frequency of the electron in the receiver is instantaneously affected. Statement is: ___ False _______

PHY-222 Classical Physics II (online) ii) The electron in the receiving antenna oscillates at a lower frequency than the electron in the transmitting antenna because of the distance between the antennas. Statement is: ___ False _______ iii) If the frequency of oscillation increases but the amplitude of the electron oscillation remains the same, then the electron in the transmitting antenna is experiencing larger accelerations (recall what you know about acceleration and motion). Statement is: ___ True _______ Explain your reasoning for your answer. Recall what you know about acceleration and motion and include in your explanation how this affects the strength of the transmitted electromagnetic signal. The electrons are moving faster as they oscillate for the frequency to increase and the amplitude to stay the same. When the electron moves faster toward its peak and then away from the peak at a new frequency, it experiences bigger change in velocity. This means that the time it took for the change to happen is less than that of the old frequency and it indicates the acceleration should be higher. iv) If the amplitude increases but frequency remains the same, the electron at the receiving antenna experiences larger peak forces but oscillates at the same frequency as before. Statement is: ___ True _______ v) If the frequency of the transmitting electron decreases by a factor of two, it will now take longer for the electromagnetic signal to reach the receiving antenna. Statement is: ____ False ______ vi) If the frequency decreases, the wavelength decreases. Statement is: ___ False _______ vii) The electromagnetic waves generated by the transmitting antenna produce currents in the receiving antenna. Statement is: ____ True ______ viii) When the electron in the transmitting antenna is at its peak height, the electron in the receiving antenna is always also at its peak height. Statement is: ____ False ______ d) For the radio wave transmitter in the simulation, which of the following orientations of the receiver antenna will pick up the signal? (Select all that will) i) An antenna oriented vertically ii) An antenna oriented horizontally (parallel to the ground) with one tip pointing towards the transmitting antenna (so it is oriented East-West) iii) An antenna oriented horizontally and perpendicular to the antenna in the previous answer (so it is oriented North-South) Correct statement is: ____ i ______

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