Homework Help: Physics

Posted by Charles on Tuesday, April 17, 2007 at 3:24am.

Please can you help out:

1)The Potential diff across the terminals of a battery is 8.5v when there is a current of 3amps in the cct from the -ve to the +ve terminal. When the current is 2amps in the reverse direction, the potential diff becomes 11volts.
a) what is the internal resistance of the battery?
b) what is the e.m.f of the battery

2) The instantaneous current I across a 200-ohm resistor is given by I= 10cos 377t
a) find the freq and the period
b) find the voltage across the resistor when t=1/240 second

At 3 amp,
8.5=emf =3r

at 2 amp
11 = emf=2r

you have two equations, two unknowns. Solve for emf and r. You can solve for rinternal directly by subtracting the equations.

On the second, frequency is in the given. remember Amplitude*cos(2PI*f*t) is the wave formula.

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