A flashlight, which uses two 1.5 V batteries in series, is turned on for 2.0 minutes. If the current in the flashlight is 100 mA, what is the energy dissipated?
A. 12 J
B. 9.0 J
C. 72 J
D. 36 J
E. 18 J
D. 36 J
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A thermocouple is made up of a spherical bead bimetallic junction at the end of two very thin wires of different materials. For example, in a type-T thermocouple, a copper wire and a constantan wire, with wire diameters ranging from 0.5 mm to 0.025 mm, are fused together to make a spherical bead that is also of a similar order-of-magnitude diameter. For such a thermocouple, determine the appropriate diameter of the spherical bead junction so as to ensure a response time of less than 2 s (?t ? 2 s) in water, which is at 40°C and has a convective heat transfer coefficient of 80 h = W/m2 K. Consider the bead junction to have properties of Cu, and to be initially at 150°C. Also, for the calculated bead diameter, what would be the response time in air at 40°C and 10 h = W/m2 K?
GIVEN • Copper and constanton wire with diameter range from 0.5 mm to 0.025 mm fused together • Response time ?t ? 2 s • Water bath temperature (T?) = 40°C • Convective heat transfer coefficient ( ch ) = 80 W/(m2 K) • Initial temperature of bead junction (T0)=1500 FIND • Appropriate diameter of spherical bead junction to ensure response time of less than 2 seconds. • Response time in air at 40°C and 10 h = W/m2 K for calculated bead diameter. ASSUMPTIONS • Constant thermal conductivity • End effects are negligible PROPERTIES AND CONSTANTS we get for Copper ks =391 W/m K c = 383 J/kg K ?=8930 kg/m3
A. The component of the curl in this direction is positive. B. The component of the curl in this direction is negative. C. The component of the curl in this direction is zero.
As more lamps are put into a parallel circuit, the overall current in the power source
A) increases. B) decreases. C) remains the same.
If the amplitude of a system moving in simple harmonic motion is doubled, which of the following quantities doesn’t change?
1.total energy 2.maximum speed 3.maximum acceleration 4.period