A portable CD player operates with a current of 23 mA at a potential difference

Question

A portable CD player operates with a current of 23 mA at a potential difference of 3.9 V. What is the power usage of the player?

How many 65-W lightbulbs can be connected in parallel across a potential difference of 90 Vbefore the total current in the circuit exceeds 2.2 A ?

What is the magnetic force exerted on a 2.15 m length of wire carrying a current of 0.919 A perpendicular to a magnetic field of 0.730 T ?

A mirrored-glass gazing globe in a garden is 35.0 cm in diameter. What is the focal length of the globe?

A concave mirror produces a virtual image that is three times as tall as the object. If the object is 18 cm in front of the mirror, what is the image distance? What is the focal length of this mirror?

Explanation / Answer

1.

Power = V*i

Using given values:

P = 3.9*23*10^-3

P = 0.0897 W = 89.7*10^-3 W = 89.7 mW

2.

P = V*I

I = P/V = 65/90 = 0.722

from kirchoff's law

Inet = I1 + I2 + I3+ .....

Since

I1 = I2 = I3 = .... = I

So,

Inet = n*I

Inet = 2.2 A

I = 0.722

n = no. of bulbs = 2.2/0.722 = 3.05

Max bulbs = 3

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