please check these:
A concave mirror with a focal length of 10.0 cm creates a real image 30.0 cm away on its principal axis. How far from the mirror is the corresponding object?
a. 20cm
b. 15cm
c. 7.5cm
d. 5.0cm
B
A diffraction grating that contains 650 472 lines/m is illuminated by monochromatic light (wavelength=632.8 nm) from a helium-neon laser directed perpendicular to the surface of the grating. At what angles would one observe the first-order and second-order maxima?
theta1=24.30degrees;theta2=55.38degrees
How is a motor's mechanical energy able to perform mechanical work?
a. mechancial energy is converted into electrical energy
b. a current is generated by a rotating loop in a magnetic field
c. electrical energy is converted into a magnetic force
d. a shaft connected to the rotating coil is attached to some external device
D
the rms current in an ac current is 3.6A. find the maximum current.
a. 5.1 A
b. 4.7 A
c. 2.8 A
d. 1.8 A
A
Which of the following statements about electromagnetic radiation is true?
a. it transfers energy to objects in the path of the electromagnetic waves
b. it can be converted to other energy forms
c. it transports the energy of electromagnetic waves
d. all of the above
B
What causes the dark lines in the absorption spectrum of an element to occur?
a. photons are absorbed when electrons jump from a higher-enegy to a lower-energy state
b.photons are emitted when electrons jump from a higher-energy to a lower-energy state
c. photons are absorbed when electrons jump from a lower-energy to a higher-energy state
d. photons are emitted when electrons jump from a lower-energy to a higher-energy state
C
What is the speed of a 50 g rock if its de Broglie wavelength is 3.32*10^-34 m?
(h=6.63*10^-34 J*s)
a. 40 m/s
b. 30 m/s
c. 20 m/s
d. 60 m/s
A
What does the mass number of a nucleus indicate?
a. the number of neutrons present
b. the number of protons present
c. the average atomic mass of the element
d. the number of neutrons and protons present
D
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