CURRENT ELECTRICITY
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FORMULA:
1) Current (I)= Charge/Time
= Q/t
= ne/t
2) Ohm's Law : V= IR
Where V= Potential difference.
I = Current
R = Resistance
3) Internal Resistance (r)=
{R(E - V)V}
Where, E= e.m.f. of a cell
V= Terminal voltage
4) Resistance in series (R)=
R₁ + R₂ + R₃ + .......
5) Resistance in parallel (1/R)=
1/R₁+ 1/R₂+ 1/R₃ + .........
I= nE/(me + R) where n is number of cells.
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1) The amount of charge passing through any point of a a of a a conductor is 0.5 coulomb in 5 second. Find the current. 0.1A
2) Find the potential difference required to pass a current of 0.2 Amp. in a distance of 20 ohm 4 Volt.
3) An electric bulb takes 1.2 Amp. current at 6 6 Volt. Find its resistance. 5
4) A resistance of 6 ohm is connected with the the cell of EMF 1.5 V and negligible internal resistance. Calculate the current flowing through it. 0.25Amp.
5) 3 cells of each each each e.m.f 1.5V and internal resistance 2ohm Q are current through the resistance ? 0.09 Amp.
6) A metallic wire has a resistance UP 20 ohm per metre. Find the total resistance of two lengths of wire, each 1.5 long, connected in parallel.
What will be the resistance of 4m of a wire of the same material but with twice the area area of cross section ? 15, 40 ohm
7) Four cell of e.m.f 1.5 V and internal resistance 2 ohm are connected to an internal resistance of 1.5 ohm in parallel. Find the current flowing in external circuit and drop in potential across the terminal of cell ?
0.5 ohm, o.75 Amp. 0.375V
8) A battery of 9 V having a negligible internal resistance, is connected to 3 resistance to 3 resistance resistance of magnitude 2, 3, and x ohm. If the current in circuit is 0.2 A. find the value of x. 40 ohm
9) A cell of e.m.f. 18V is connected to an external resistance of 2 ohm when potential difference recorded at its terminal is 1.6 V. Find the internal resistance of of cell. 0.25 ohm
10) 24 cells each of e.m.f. 2 volt, internal resistance 1.5 ohm are to be connected to provide maximum current through a load of resistance 4 ohm. How will you connect them? What will be the current in the load? 2 Amp. We shall connect 3 rows in parallel, each row having 8 fellin series.
11) The terminal voltage of a cell of e.m.f. 4V is 3V. Find the current in the circuit and internal resistance, if external resistance is 5 ohm. 1.67 ohm
12) The e.m.f. of a d.c. dynamo is 240 V. it can give a maximum current of 25A. When operated for 5 hours hours under the condition calculate
A) the energy generated 30kWh
B) the total charge transferred. 4.5x 10⁵ C
13) Two cells, each having an e.m.f. of 2V and an internal resistance 1.5 ohm are connected in parallel. The arrangement is then connected to a 4.25 ohm register. Calculate the current flowing in the 4.25 ohm resistor. 0.4A
14) Rewrite the following sentence using the correct alternative : A fuse is connected in parallel/ series to the earth/ neutral/ live wire.
Ans) A fuse is connected in series to the earth with the live wire.
15) Potential difference between two points its of a wire carrying 2 amphere current is 0.1 volt. Calculate the resistance between these points. 0.05 ohm
16) A simple electric circuit has has a 24V battery and resistor of 60 ohm. What will be the current in the current in the circuit? The resistances of the connecting wires are negligible. 0.4 Amp
17) Find the total resistance three resistors, each of 3 ohm, connected in parallel. 1 ohm
18) You are given three resistance of 2, 4 and 6 om. Find the resultant resistance when these these are connected in
A) parallel. 1.09 ohm
B) series 12 ohm
19) Two resistances when connected in parallel give the resultant value of 2 ohm. When connected in series the value becomes 9 ohms. Calculate the value of each resistance. 3 or 6
20) A torch bulb when cold has 152 resistance. It draws a current 0.3 A. When glowing from a source of 3V. Calculate the resistance of bulb when glowing and explain the reason for the difference in the resistance. 10 ohm.
The reason for the difference in resistance when cold and when it glows is that the resistance of the filament of bulb increase with the increase in temperature.
21) Calculate the resistance of 1km long copper wire of radius 1 mm.( resistivity of copper is 1..72/10³). 5.5 ohm
22) When a potential difference 2 volt in applied across the ends of a wire of 5 metre length, a current of 1A is found to flow through it calculate
A) resistance per unit length of wire. 2, .4 ohm
B) the resistance of 2m length of this wire wire the resistance across the ends ware. 0.8 ohm
C) the resistance across the ends of wire it is doubled on itself. 0.5
23) Two copper wire A and B of length 30m and 10 m have radius 2mm and 1mm respectively. compare the resistance of two wires which will have less resistance. 3/4. The wire A has less resistance.
24) A high resistance Voltameter is connected to a dry cell battery. The Voltameter reads 9.0V.A 24 resistance is connected across the terminal of the battery and the Voltameter reading become 7.2V. Calculate the internal resistance of battery . 6 ohm
25) A cell supplies a current of 2A when it is connected to a resistor of resistance 5 ohm and supplies a current 1.2A. If it is connected to a Resistor of resistance 9 ohm. Find e.m.f. and internal resistance of cell. 12 volt
26) A cell o1.5 volt and internal resistance 2 ohm is connected across a resistor of 2 ohm find the current what would be the current if two such cells were connected were connected
A) in series. 0.5A
B) in parallel. 0.5A
Draw circuit diagram in each case.
27) Four cells each of e.m.f 2V and internal resistance 0.1 ohm are connected in series. The combination is series is joined to an ammeter of negligence resistance, a 1.6 ohm resistors and an unknown resistor R'. The current in circuit is 2A. Draw a labelled diagram for above arrangements an and calculate
A) total resistance in the circuit.
B) total emf. 0.4ohm, 8V
C) the value of R'. 2 ohm
D) P. D across R'. 4V
3) How can three resistance of 2, 3 6 ohm resistor connected to give a total resistance of 1 omega.
4) You are given one 12 omega and two 6 omega resistors. How would you connect them below an effective resistance of
i) 24 omega
ii) 15 omega
iii) 2.4 omega
iv) 10.0 omega
Draw relevant diagram.
5) Find the total resistance of 3 resistors, each of 3 ohm, connected in parallel.
6) You are given three resistance of 2, 4, and 6 ohm. Find the resultant resistance when these are connected in
i) parallels
ii) series.
7) Two resistances when connected in parallel give the resultant value of 2 Ohm. When connected in series the value becomes 9 ohms. Calculate the value of each resistance.
9) How can three resistance of 2, 3, 6 ohms be connected to give a total resistance of 1 omega.
10) Two resistors in series have resistance of 9 Ohms and in parallel a resistance of 2 Ohms. Compute the individual resistance
11) What resistance must be joined with a 24 ohms resistor in order to make a combined resistance of 8 ohms ? How must the resistance be joined ?
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