For an ideal battery (r = 0 ), closing the switch in FIGURE P28.54 does not affect

For an ideal battery (r = 0 Ω), closing the switch in FIGURE P28.54 does not affect the brightness of bulb A. In practice, bulb A dims just a little when the switch closes. To see why, assume that the 1.50 V battery has an internal resistance r = 0.50 Ω and that the resistance of a glowing bulb is R = 6.00 Ω.

a. What is the current through bulb A when the switch is open?b. What is the current through bulb A after the switch has closed?c. By what percentage does the current through A change when the switch is closed?

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A FIGURE P28.54