Camera Exposure: The focal length of a camera lens is 40 mm and its aperture diameter is 10 mm. What is the f-number of this lens?
A. 4.0
B. 2.0
C. 5.6
D. 0.25
E. 0.40
Answer: A
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Which of the following processes slowed the collapse of protogalactic clouds?
A) the conversion of gravitational potential energy into kinetic and thermal energy as the cloud collapsed B) the formation of the first generation of stars C) the shock waves from the exploding supernovae of the earliest stars D) the pull of gravity of the mass of the cloud material E) the radiating away of thermal energy
A high-voltage powerline operates at 500000 V-rms and carries an rms current of 500 A. If the resistance of the cable is 0.050?/km, what is the resistive power loss in 200 km of the powerline?
a. 250 kW b. 500 kW c. 1 Megawatt d. 2.5 Megawatts e. 250 Megawatts
An electron is accelerated through a potential difference of 25 000 V. What is the de Broglie wavelength of the electron (in m)?
a. 5.9 × 10^-12 b. 6.8 × 10^-12 c. 6.5 × 10^-12 d. 7.8 × 10^-12 e. 5.5 × 10^-12
The speed of a bullet fired from a gun will be about the same as the speed of the recoiling gun
A) when momentum is conserved. B) because velocity is conserved. C) when both velocity and momentum are conserved. D) if the masses of the bullet and gun are equal. E) none of the above