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Current Electricity â?– Illustrative Examples 1) A 4.0 m long wire has diameter of 0.30 mm. If its resistance is 30Q, find its resistivity and conductivity. Data: R = 30
,
= 4.0 m r = 0.3/2 = 0.15
10-3m
(Ans.:
)
2) How much work is done in moving a charge of 3.0 coulomb from a point at 120 V to a point at 200 V? Data: p. d. = (200-1``20)V, q = 3 coulombs 3) A resistor of l0
(Ans.: W = 240 J)
connected across a cell of emf l2 V. draws the current of 1.1 A. find
the internal resistance of the cell. Data: E = l2V, R = l0
, l = l.l A, r = ?
(Ans.: r = 0.91
)
4) In an electric circuit, p. d. across resistor is 10 V and current flowing through it is 0.5 A. Find (i) resistance and (ii) charge flown through resistor for 30 second. Data: V = 10V, I = 0.5A, t = 30s. 5) A platinum wire has resistance of 2.5
(Ans.: q = 15 C) at 00C. If its temperature coefficient of
resistance is 4x10-3 / 0C, find the resistance of wire at 700C. Data: R0 = 2.5
,
= 0.004/0C ,(t-0) = t = 700C.
(Ans.: Rt = 3.2
)
6) An electric iron draws a current of 3.0 A from 230 V supply line. What current will it draw when connected to 110 V supply line? Assume that its resistance does not change significantly. Data: V1 = 230V ,I1=3A, R = ? V2 = 110V I2 = ? (Ans.: R = 76.66
, I2 = 1.435 A)
7) Two cells of each 1.5 V and third cell of 1 V are connected in series. Find the battery voltage. Data: Cell voltage = 1.5 V and 1 V.
(Ans.: V = 4V)
8) The heating element connected to 220 V draws a current of 4 A. Determine the amount of heat dissipated in 15 minute. (J = 4.2 J/cal) Data: V = 220 V, I = 4 A, t = 15 min. = 15
60s, j = 4.2 J/cal, H = ? (Ans.: H = 1.88
9)
calorie)
A refrigerator has power rating of 250 watt, which operates for 8 hours a day. Calculate the cost of electrical energy to operate it for a month of 30 days. The cost of electrical energy is Rs. 3 per kWh. (Assume that there is no load shading or power cut). Data: p = 250 W = 0.25 kW, t = 8 hours (Ans.: cost of 60 kwh electricity = Rs. 180)
F.Y.J.C. Science
Current Electricity