Force on a Wire: A wire is carrying current vertically downward. What is the direction of the force on this wire due to Earth's magnetic field?
A. horizontally towards the north
B. horizontally towards the south
C. horizontally towards the east
D. horizontally towards the west
E. vertically upward
Answer: C
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Suppose two charges, one positive and one negative, are separated by a distance d. Where can two equipotential surfaces at different potentials intersect in the region near the charges?
a. halfway between the charges if the charges have the same magnitude b. closer to the smaller negative charge than the larger positive charge if the charges are not equal c. Equipotential surfaces at different potentials cannot intersect. d. closer to the smaller positive charge than the larger negative charge if the charges are not equal
If 5.0 × 10^21 electrons pass through a 20-? resistor in 10 min, what is the potential difference across the resistor?
a. 21 V b. 32 V c. 27 V d. 37 V e. 54 V
Light of wavelength 500 nm illuminates a round 0.50-mm diameter hole. A screen is placed 6.3 m behind the slit. What is the diameter of the central bright area on the screen?
A) 15 mm B) 270 ?m C) 7.7 mm D) 3800 ?m
Only 10% of the energy dissipated by the tungsten filament of an incandescent lamp is in the form of useful visible light. Consider a 100 W lamp with a 10 cm spherical glass bulb. Assuming an emissivity of 0.85 for the glass and ambient air temperature of 20°C, what is the temperature of the glass bulb?
GIVEN
• A spherical glass light bulb in air
• Bulb power consumption (P) = 100 W
• 10% of energy is in the form of visible light
• Diameter (D) = 10 cm = 0.1 m
• Bulb emissivity (?) = 0.85
• Ambient temperature (T?) = 20°C = 293 K
FIND
• The temperature of the glass bulb (Ts)
ASSUMPTIONS
• Ambient air is till
• The bulb has reached steady state
• The surrounding behave as a black body at T?
SKETCH
PROPERTIES AND CONSTANTS
Boltzmann constant (?) = 5.7 × 10–8 W/(m2 K4).