A 50 mm × 45 mm × 20 mm cell phone charger has a surface temperature of Ts = 33°C when plugged into an electrical wall outlet but not in use. The surface of the charger is of emissivity ε = 0.92 and is subject to a free convection heat transfer coeffcient of h = 4.5 W/m2 ⋅K. The room air and wall temperatures are T[infinity] = 22°C and Tsur = 20°C, respectively. If electricity costs C = $0.18/kW ⋅ h, determine the daily cost of leaving the charger plugged in when not in use.

Aloaded platform of total mass 500 kg is supported by a dashpot and by a set of springs of effective stiffness 72 kn/m. it is observed that when the platform is depressed through a distance x = 12.5 cm below its equilibrium position and then released without any initial velocity; it reaches its equilibrium position in the shortest possible time without overshoot. find the position and velocity of the loaded platform 0.10 sec. after its release. if a further load of 400 kg is added to the platform, find, i) the frequency of damped vibrations, and i) the amplitude of vibration after 2 complete oscillations, given that the initial amplitude is 15 cm.

Consider a large isothermal enclosure that is maintained at a uniform temperature of 2000 k. calculate the emissive power of the radiation that emerges from a small aperture on the enclosure surface. what is the wavelength ? , below which 10% of the emission is concentrated? what is the wavelength ? 2 above which 10% of the emission is concentrated? determine the wavelength at which maximum spectral emissive power occurs. what is the irradiation incident on a small object placed inside the enclosure?

The short distance from the objective lens to the object causes problems at high magnification. which of the following is the most serious? a. cleaning the object surface b. positioning the object c. reflection from the object surface. d. illumination of the object