Physics Electromagnetic Waves Level: High School
At what distance from a 50 W electromagnetic wave point source (like a light bulb) is he amplitude of the electric field 24 V/m ? micro 0 c = 376.991 ohm .
Physics Current Electricity Level: High School
Dc circuits
An inductor and a resistor are connected with a double pole switch to a battery as shown in the figure .The switch has been in position b for a long period of time . If the switch is thrown from position b to position a (connecting the battery) , how much time elapses current reaches 219 mA ? Answer in units of ms .
a) What is the maximum current in the inductor a long time after the switch is in position a ?
b) The switch has brushes within so that the switch can be thrown from a to b without internal sparking . Now the switch is smoothly thrown from a to b , shorting the inductor and resistor . How much time elapses before the current falls to 92 mA ?
Question Diagram
Physics Electromagnetic Induction Level: High School
A bar magnet is held above the center of a conducting wire loop in a horizontal plane with the north end of the magnet toward the loop . The magnet is dropped . Find the direction of the current , as viewed from the above , around the wire loop while the magnet is falling toward the loop .a) Counter clockwise
b) clockwise
c) Unable to determine the direction
Find the direction of the current around the loop after the magnet has passed through the wire loop and moves away from it .1) Unable to determine the direction
2) Counter-clockwise
3) Clockwise
Question Diagram
Physics Electromagnetic Induction Level: High School
A straight , horizontal wire of length l, mass M , and resistance R falls vertically without friction or air drag along parallel vertical conducting rails of negligible resistance , as shown (assume this wire remains in constant with the rails as it falls) . The rails are connected at the bottom by a horizontal rail (of zero resistance ) ,so that the wire and rails form a closed rectangular loop . A uniform horizontal field B perpendicular to the wire exists throughout the region . What is terminal velocity v of the wire , ie , the eventual steady-state speed reached by the wire ?1) v = B2l/ M g
2) v = M g / B l
3) v = M g R / B2 l2
4) v = M g R2 / B2 l3
5) v = M g / B2 l
a) After a long time , what is the current I in the loop ?
b) What is the electrical power P produced in the loop after a long time ?
c) The power produced by gravity acting on the wire when it is falling at the terminal velocity is .
1) zero
2) equal to the electrical power .
3) greater than the electrical power .
4) less than the electrical power .
5) either greater or less than the electric power , depending on the magnitude of B .
Question Diagram
Physics Electromagnetic Induction Level: High School
Electromotive force
A copper bar has a constant velocity in the plane of the paper and perpendicular to a magnetic field pointed into the plane of the paper . If the bar is moving from left to right (=>), how are charges distributed on the bar ?
1) The top will be positive and the bottom will be negative .
2) Both the top and the bottom of the bar will be positive .
3) The top will be negative and the bottom will be positive .
4) Both the top and bottom of the bar will be negative .
Question Diagram
Physics Electromagnetic Induction Level: High School
A flexible loop of conducting wire has a radius of 15 cm and is in a magnetic field of strength of 0.21 T . The loop is grasped at opposite ends and stretched until it closes to an area of 0.005 m^2 . If it takes 0.23 s to close the loop , find the magnitude of the average induced emf in it during this time . Answer in units of mV .Question Diagram
Physics Electromagnetic Induction Level: High School
A circular coil of wire rests on your desk. A magnetic field is directed at right angles to the plane of your desk and passes through the coil, for a clockwise current (as you look down on your desk) to be generated, the magnetic coil field must be directed
1) upward away from the desk and be constant in time .
2) upward away from the desk and be increasing in time .
3) downward toward the desk and be constant in time .
4) downward toward the desk and be increasing in time .
Physics Electromagnetic Induction Level: High School
A flat coil of wire consisting of 21 turns , each with an area of 40 cm^2 , is positioned perpendicularly to a uniform magnetic field that increases its magnitude at a constant rate from 3.4 T to 11 T in 3.3 s . If the coils has a total resistance of 0.21 ohm , what is the magnitude of the induced current ? Answer in units of a .
Physics Electromagnetic Induction Level: High School
The plane of a rectangular coil, 4.7 cm by 8.1 cm , is perpendicular to the direction of a uniform magnetic filed B . If the coil has 56 turns and a total resistance of 11.3 ohm , at what rate must the magnitude of B change to induce a current of 0.13 A in the windings of the coil ? Answer in units of T/s
Physics Electromagnetic Waves Level: High School
In the diagram on the right , the electric field vector points upwards and the magnetic field vector points out of the page directly at you . This electromagnetic wave is traveling .a) upwards
b) downwards
c) to the right
d) into the page
Physics Ray Optics Level: High School
polarization
The figure at below shows a set of polaroids arranged so that initially unpolarized light of intensity Io passes through them in succession (#1 through #4 in order), Polaroid # 1 has a vertical transmission axis , and each successive polaroid is rotated by an angle of theta = 90 degree/3 = 30 degree with respect to the previous one , This means that polaroid #4 has a horizontal transmission axis .
a) What is the intensity of the light in the region between polaroids #2 and #3 , in terns of Io ?
b) What is the intensity of the light after it passes through polaroid #4 , in terms of Io ?
Question Diagram
Physics Electromagnetic Induction Level: High School
The picture on the right shows a metal rod of mass m and length (that slides along two frictionless rods which are connected by a resistor R to form a complete circuit , with a uniform magnetic field B perpendicular to the plane of the circuit (this could , for example , be Earth’s magnetic field ), As the rod falls , the area of the circuit increases the magnetic force on the rod , which is directed upward . Find the terminal speed of the rod .Question Diagram
Physics Magnetism,Magnetic Effects Of Current Level: High School
Force on a charged particle in a magnetic field
A proton is passed through a velocity selector made up of a two charged plates that create a uniform vertical electric field E , and a uniform magnetic field B that points into the page (see diagram) . If the magnitude of B is 2 m T , what should the magnitude of the electric field be if we wish for particles with a speed of 2 x 10^6 m/s to pass undeflected through the apparatus ? which of the plates must be positively charged ?
Question Diagram
Physics Electromagnetic Induction Level: High School
The graph below shows the magnitude of B of a magnetic field that passes through a fixed loop in a direction perpendicular to the loop . The current generated in the loop is a maximum at t =a) 0 s
b) 1 s
c) 3 s
d) 6 s
Question Diagram
Physics Electromagnetic Induction Level: High School
A transformer has 1000 turns in its primary and 25 turns in its secondary. The primary is connected to a 120 V, 60 Hz source. The secondary is connected to a 0.6 resistor. Show that the current, to the nearest thousandth of an amp is .174 A, that flows in the primary if this transformer is 72% efficient.
