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Page 1 JEE Solved Examples on Current Electricity JEE Mains Q1: In the Bohr's model of hydrogen atom, the electrons moves around the nucleus in a circular orbit of a radius ?? × ???? -???? metre. It's time period is ?? . ?? × ???? -???? ?????? . The current associated is (a) Zero (b) ?? . ?? × ???? -???? ?? (c) ?? . ???? ?? (d) ?? . ???? × ???? -?? ?? Ans: (d) ?? = ?? ?? = 1.6×10 -19 1.5×10 -16 = 1.07 × 10 -3 A Q2: A copper wire of length ?? ?? and radius ?? ???? is joined in series with an iron wire of length ?? ?? and radius ?? ???? and a current is passed through the wire. The ratio of current densities in the copper and iron wire is (a) ???? : ?? (b) ?? : ?? (c) ?? : ?? (d) ?? : ?? Ans: (b) We know ?? = ?? ?? when ?? = constant ?? ? 1 ?? ? ?? ?? ?? ?? = ?? ?? ?? ?? = ( ?? ?? ?? ?? ) 2 = ( 3 1 ) 2 = 9 1 Q3: 8 In a wire of circular cross-section with radius ?? , free electrons travel with a drift velocity ?? , when a current ?? flows through the wire. What is the current in another wire of half the radius and of the some material when the drift velocity is ?? ?? (a) ?? ?? (b) ?? (c) ?? /?? (d) ?? /?? Ans: (c) ?? = ?????? ?? ?? = ?????? ?? 2 ?? and ?? 2 = ?????? ( ?? 2 ) 2 · 2?? = ?????? · 2 ?? 2 = ?? 2 Q4: Two wires ?? and ?? of the same material, having radii in the ratio ?? : ?? and carry currents in the ratio ?? : ?? . The ratio of drift speeds of electrons in ?? and ?? is (a) ???? : ?? (b) ?? : ???? (c) ?? : ?? (d) ?? : ?? Ans: (a) As ?? = ?????? ?? ?? ? ?? 1 ?? 2 = ?? 1 ?? 2 × ?? ?? 1 ?? ?? 2 = ?? 1 2 ?? 2 2 · ?? ?? 1 ?? ?? 2 ? ?? ?? 1 ?? ?? 2 = 16 1 Page 2 JEE Solved Examples on Current Electricity JEE Mains Q1: In the Bohr's model of hydrogen atom, the electrons moves around the nucleus in a circular orbit of a radius ?? × ???? -???? metre. It's time period is ?? . ?? × ???? -???? ?????? . The current associated is (a) Zero (b) ?? . ?? × ???? -???? ?? (c) ?? . ???? ?? (d) ?? . ???? × ???? -?? ?? Ans: (d) ?? = ?? ?? = 1.6×10 -19 1.5×10 -16 = 1.07 × 10 -3 A Q2: A copper wire of length ?? ?? and radius ?? ???? is joined in series with an iron wire of length ?? ?? and radius ?? ???? and a current is passed through the wire. The ratio of current densities in the copper and iron wire is (a) ???? : ?? (b) ?? : ?? (c) ?? : ?? (d) ?? : ?? Ans: (b) We know ?? = ?? ?? when ?? = constant ?? ? 1 ?? ? ?? ?? ?? ?? = ?? ?? ?? ?? = ( ?? ?? ?? ?? ) 2 = ( 3 1 ) 2 = 9 1 Q3: 8 In a wire of circular cross-section with radius ?? , free electrons travel with a drift velocity ?? , when a current ?? flows through the wire. What is the current in another wire of half the radius and of the some material when the drift velocity is ?? ?? (a) ?? ?? (b) ?? (c) ?? /?? (d) ?? /?? Ans: (c) ?? = ?????? ?? ?? = ?????? ?? 2 ?? and ?? 2 = ?????? ( ?? 2 ) 2 · 2?? = ?????? · 2 ?? 2 = ?? 2 Q4: Two wires ?? and ?? of the same material, having radii in the ratio ?? : ?? and carry currents in the ratio ?? : ?? . The ratio of drift speeds of electrons in ?? and ?? is (a) ???? : ?? (b) ?? : ???? (c) ?? : ?? (d) ?? : ?? Ans: (a) As ?? = ?????? ?? ?? ? ?? 1 ?? 2 = ?? 1 ?? 2 × ?? ?? 1 ?? ?? 2 = ?? 1 2 ?? 2 2 · ?? ?? 1 ?? ?? 2 ? ?? ?? 1 ?? ?? 2 = 16 1 Q5: Two wires of resistance ?? ?? and ?? ?? have temperature co-efficient of resistance ?? ?? and ?? ?? respectively. These are joined in series. The effective temperature co -efficient of resistance is (a) ?? ?? +?? ?? ?? (b) v ?? ?? ?? ?? (c) ?? ?? ?? ?? +?? ?? ?? ?? ?? ?? +?? ?? (d) v?? ?? ?? ?? ?? ?? ?? ?? v?? ?? ?? +?? ?? ?? Ans: (c) Suppose at ?? ° C resistances of the two wires becomes ?? 1?? and ?? 2?? respectively and equivalent resistance becomes ?? ?? . In series grouping ?? ?? = ?? 1?? + ?? 2?? , also ?? 1?? = ?? 1 (1 + ?? 1 ?? ) and ?? 2?? = ?? 2 (1 + ?? 2 ?? ) ?? ?? = ?? 1 (1 + ?? 1 ?? ) + ?? 2 (1 + ?? 2 ?? ) = (?? 1 + ?? 2 ) + (?? 1 ?? 1 + ?? 2 ?? 2 )?? = (?? 1 + ?? 2 )[1 + ?? 1 ?? 1 + ?? 2 ?? 2 ?? 1 + ?? 2 ?? ] . Hence effective temperature co -efficient is ?? 1 ?? 1 +?? 2 ?? 2 ?? 1 +?? 2 . Q6: A rod of certain metal is ?? ?? long and ?? . ?? ???? in diameter. It's resistance is ?? × ???? -?? ?? . A disc of the same metal is ?? ???? thick and ?? ???? in diameter, what is the resistance between it's circular faces. (a) ?? . ???? × ???? -?? ?? (b) ?? . ?? × ???? -?? ?? (c) ?? . ???? × ???? -?? ?? (d) ?? . ?? × ???? -?? ?? Ans: (b) By using ?? = ?? · ?? ?? ; ?? disc ?? rod = ?? disc ?? rod × ?? rod ?? disc ? ?? disc 3×10 -3 = 10 -3 1 × ?? (0.3×10 -2 ) 2 ?? (10 -2 ) 2 ? ?? disc = 2.7 × 10 -7 O. Q7: If a copper wire is stretched to make it ?? . ?? % longer, the percentage increase in resistance will be (a) 0.2 (b) 2 (c) 1 (d) 0.1 Ans: (a) In case of streching ?? ? ?? 2 So ??? ?? = 2 ??? ?? = 2 × 0.1 = 0.2 Q8: Equal potentials are applied on an iron and copper wire of same length. In order to have same current flow in the wire, the ratio ( ?? iron ?? copper ) of their radii must be [Given that specific resistance of iron = ?? . ?? × ???? -?? ???? and that of copper = ?? . ?? × ???? -?? ???? ] (a) About 1.2 (b) About 2.4 (c) About 3.6 (d) About 4.8 Page 3 JEE Solved Examples on Current Electricity JEE Mains Q1: In the Bohr's model of hydrogen atom, the electrons moves around the nucleus in a circular orbit of a radius ?? × ???? -???? metre. It's time period is ?? . ?? × ???? -???? ?????? . The current associated is (a) Zero (b) ?? . ?? × ???? -???? ?? (c) ?? . ???? ?? (d) ?? . ???? × ???? -?? ?? Ans: (d) ?? = ?? ?? = 1.6×10 -19 1.5×10 -16 = 1.07 × 10 -3 A Q2: A copper wire of length ?? ?? and radius ?? ???? is joined in series with an iron wire of length ?? ?? and radius ?? ???? and a current is passed through the wire. The ratio of current densities in the copper and iron wire is (a) ???? : ?? (b) ?? : ?? (c) ?? : ?? (d) ?? : ?? Ans: (b) We know ?? = ?? ?? when ?? = constant ?? ? 1 ?? ? ?? ?? ?? ?? = ?? ?? ?? ?? = ( ?? ?? ?? ?? ) 2 = ( 3 1 ) 2 = 9 1 Q3: 8 In a wire of circular cross-section with radius ?? , free electrons travel with a drift velocity ?? , when a current ?? flows through the wire. What is the current in another wire of half the radius and of the some material when the drift velocity is ?? ?? (a) ?? ?? (b) ?? (c) ?? /?? (d) ?? /?? Ans: (c) ?? = ?????? ?? ?? = ?????? ?? 2 ?? and ?? 2 = ?????? ( ?? 2 ) 2 · 2?? = ?????? · 2 ?? 2 = ?? 2 Q4: Two wires ?? and ?? of the same material, having radii in the ratio ?? : ?? and carry currents in the ratio ?? : ?? . The ratio of drift speeds of electrons in ?? and ?? is (a) ???? : ?? (b) ?? : ???? (c) ?? : ?? (d) ?? : ?? Ans: (a) As ?? = ?????? ?? ?? ? ?? 1 ?? 2 = ?? 1 ?? 2 × ?? ?? 1 ?? ?? 2 = ?? 1 2 ?? 2 2 · ?? ?? 1 ?? ?? 2 ? ?? ?? 1 ?? ?? 2 = 16 1 Q5: Two wires of resistance ?? ?? and ?? ?? have temperature co-efficient of resistance ?? ?? and ?? ?? respectively. These are joined in series. The effective temperature co -efficient of resistance is (a) ?? ?? +?? ?? ?? (b) v ?? ?? ?? ?? (c) ?? ?? ?? ?? +?? ?? ?? ?? ?? ?? +?? ?? (d) v?? ?? ?? ?? ?? ?? ?? ?? v?? ?? ?? +?? ?? ?? Ans: (c) Suppose at ?? ° C resistances of the two wires becomes ?? 1?? and ?? 2?? respectively and equivalent resistance becomes ?? ?? . In series grouping ?? ?? = ?? 1?? + ?? 2?? , also ?? 1?? = ?? 1 (1 + ?? 1 ?? ) and ?? 2?? = ?? 2 (1 + ?? 2 ?? ) ?? ?? = ?? 1 (1 + ?? 1 ?? ) + ?? 2 (1 + ?? 2 ?? ) = (?? 1 + ?? 2 ) + (?? 1 ?? 1 + ?? 2 ?? 2 )?? = (?? 1 + ?? 2 )[1 + ?? 1 ?? 1 + ?? 2 ?? 2 ?? 1 + ?? 2 ?? ] . Hence effective temperature co -efficient is ?? 1 ?? 1 +?? 2 ?? 2 ?? 1 +?? 2 . Q6: A rod of certain metal is ?? ?? long and ?? . ?? ???? in diameter. It's resistance is ?? × ???? -?? ?? . A disc of the same metal is ?? ???? thick and ?? ???? in diameter, what is the resistance between it's circular faces. (a) ?? . ???? × ???? -?? ?? (b) ?? . ?? × ???? -?? ?? (c) ?? . ???? × ???? -?? ?? (d) ?? . ?? × ???? -?? ?? Ans: (b) By using ?? = ?? · ?? ?? ; ?? disc ?? rod = ?? disc ?? rod × ?? rod ?? disc ? ?? disc 3×10 -3 = 10 -3 1 × ?? (0.3×10 -2 ) 2 ?? (10 -2 ) 2 ? ?? disc = 2.7 × 10 -7 O. Q7: If a copper wire is stretched to make it ?? . ?? % longer, the percentage increase in resistance will be (a) 0.2 (b) 2 (c) 1 (d) 0.1 Ans: (a) In case of streching ?? ? ?? 2 So ??? ?? = 2 ??? ?? = 2 × 0.1 = 0.2 Q8: Equal potentials are applied on an iron and copper wire of same length. In order to have same current flow in the wire, the ratio ( ?? iron ?? copper ) of their radii must be [Given that specific resistance of iron = ?? . ?? × ???? -?? ???? and that of copper = ?? . ?? × ???? -?? ???? ] (a) About 1.2 (b) About 2.4 (c) About 3.6 (d) About 4.8 Ans: (b) ?? = constant., ?? = constant. So ?? = constant ? ?? ?? ?? ?? ?? ?? = ?? ???? ?? ???? ?? ???? ? ?? ?? ?? ?? ?? ?? 2 = ?? ???? ?? ???? ?? ???? 2 ? ?? ?? ?? ???? = v ?? ?? ?? ???? = v 1.0 × 10 -7 1.7 × 10 -8 = v 100 17 ˜ 2.4 Q9: Masses of three wires are in the ratio ?? : ?? : ?? and their lengths are in the ratio ?? : ?? : ?? . The ratio of their electrical resistance is (a) ?? : ?? : ?? (b) ?? : ?? : ?? (c) ?? : ???? : ?????? (d) ?????? : ???? : ?? Ans: (d) ?? = ?? ?? ?? = ?? ?? 2 ?? = ?? ?? 2 ?? ?? (? ?? = ?? ?? ) ?? 1 : ?? 2 : ?? 3 = ?? 1 2 ?? 1 : ?? 2 2 ?? 2 : ?? 3 2 ?? 3 = 25: 9 3 : 1 5 = 125: 15: 1 Q10: Two resistance ?? ?? and ?? ?? provides series to parallel equivalents as ?? ?? then the correct relationship is (a) ( ?? ?? ?? ?? ) ?? + ( ?? ?? ?? ?? ) ?? = ?? ?? (b) ( ?? ?? ?? ?? ) ?? /?? + ( ?? ?? ?? ?? ) ?? /?? = ?? ?? /?? (c) ( ?? ?? ?? ?? ) + ( ?? ?? ?? ?? ) = ?? (d) ( ?? ?? ?? ?? ) ?? /?? + ( ?? ?? ?? ?? ) ?? /?? = ?? ?? /?? Ans: (d) Series resistance ?? ?? = ?? 1 + ?? 2 and parallel resistance ?? ?? = ?? 1 ?? 2 ?? 1 +?? 2 ? ?? ?? ?? ?? = (?? 1 +?? 2 ) 2 ?? 1 ?? 2 = ?? ? ?? 1 + ?? 2 v?? 1 ?? 2 = v ?? ? v?? 1 2 v?? 1 ?? 2 + v?? 2 2 v?? 1 ?? 2 = v ?? ? v ?? 1 ?? 2 + v ?? 2 ?? 1 = v ?? Page 4 JEE Solved Examples on Current Electricity JEE Mains Q1: In the Bohr's model of hydrogen atom, the electrons moves around the nucleus in a circular orbit of a radius ?? × ???? -???? metre. It's time period is ?? . ?? × ???? -???? ?????? . The current associated is (a) Zero (b) ?? . ?? × ???? -???? ?? (c) ?? . ???? ?? (d) ?? . ???? × ???? -?? ?? Ans: (d) ?? = ?? ?? = 1.6×10 -19 1.5×10 -16 = 1.07 × 10 -3 A Q2: A copper wire of length ?? ?? and radius ?? ???? is joined in series with an iron wire of length ?? ?? and radius ?? ???? and a current is passed through the wire. The ratio of current densities in the copper and iron wire is (a) ???? : ?? (b) ?? : ?? (c) ?? : ?? (d) ?? : ?? Ans: (b) We know ?? = ?? ?? when ?? = constant ?? ? 1 ?? ? ?? ?? ?? ?? = ?? ?? ?? ?? = ( ?? ?? ?? ?? ) 2 = ( 3 1 ) 2 = 9 1 Q3: 8 In a wire of circular cross-section with radius ?? , free electrons travel with a drift velocity ?? , when a current ?? flows through the wire. What is the current in another wire of half the radius and of the some material when the drift velocity is ?? ?? (a) ?? ?? (b) ?? (c) ?? /?? (d) ?? /?? Ans: (c) ?? = ?????? ?? ?? = ?????? ?? 2 ?? and ?? 2 = ?????? ( ?? 2 ) 2 · 2?? = ?????? · 2 ?? 2 = ?? 2 Q4: Two wires ?? and ?? of the same material, having radii in the ratio ?? : ?? and carry currents in the ratio ?? : ?? . The ratio of drift speeds of electrons in ?? and ?? is (a) ???? : ?? (b) ?? : ???? (c) ?? : ?? (d) ?? : ?? Ans: (a) As ?? = ?????? ?? ?? ? ?? 1 ?? 2 = ?? 1 ?? 2 × ?? ?? 1 ?? ?? 2 = ?? 1 2 ?? 2 2 · ?? ?? 1 ?? ?? 2 ? ?? ?? 1 ?? ?? 2 = 16 1 Q5: Two wires of resistance ?? ?? and ?? ?? have temperature co-efficient of resistance ?? ?? and ?? ?? respectively. These are joined in series. The effective temperature co -efficient of resistance is (a) ?? ?? +?? ?? ?? (b) v ?? ?? ?? ?? (c) ?? ?? ?? ?? +?? ?? ?? ?? ?? ?? +?? ?? (d) v?? ?? ?? ?? ?? ?? ?? ?? v?? ?? ?? +?? ?? ?? Ans: (c) Suppose at ?? ° C resistances of the two wires becomes ?? 1?? and ?? 2?? respectively and equivalent resistance becomes ?? ?? . In series grouping ?? ?? = ?? 1?? + ?? 2?? , also ?? 1?? = ?? 1 (1 + ?? 1 ?? ) and ?? 2?? = ?? 2 (1 + ?? 2 ?? ) ?? ?? = ?? 1 (1 + ?? 1 ?? ) + ?? 2 (1 + ?? 2 ?? ) = (?? 1 + ?? 2 ) + (?? 1 ?? 1 + ?? 2 ?? 2 )?? = (?? 1 + ?? 2 )[1 + ?? 1 ?? 1 + ?? 2 ?? 2 ?? 1 + ?? 2 ?? ] . Hence effective temperature co -efficient is ?? 1 ?? 1 +?? 2 ?? 2 ?? 1 +?? 2 . Q6: A rod of certain metal is ?? ?? long and ?? . ?? ???? in diameter. It's resistance is ?? × ???? -?? ?? . A disc of the same metal is ?? ???? thick and ?? ???? in diameter, what is the resistance between it's circular faces. (a) ?? . ???? × ???? -?? ?? (b) ?? . ?? × ???? -?? ?? (c) ?? . ???? × ???? -?? ?? (d) ?? . ?? × ???? -?? ?? Ans: (b) By using ?? = ?? · ?? ?? ; ?? disc ?? rod = ?? disc ?? rod × ?? rod ?? disc ? ?? disc 3×10 -3 = 10 -3 1 × ?? (0.3×10 -2 ) 2 ?? (10 -2 ) 2 ? ?? disc = 2.7 × 10 -7 O. Q7: If a copper wire is stretched to make it ?? . ?? % longer, the percentage increase in resistance will be (a) 0.2 (b) 2 (c) 1 (d) 0.1 Ans: (a) In case of streching ?? ? ?? 2 So ??? ?? = 2 ??? ?? = 2 × 0.1 = 0.2 Q8: Equal potentials are applied on an iron and copper wire of same length. In order to have same current flow in the wire, the ratio ( ?? iron ?? copper ) of their radii must be [Given that specific resistance of iron = ?? . ?? × ???? -?? ???? and that of copper = ?? . ?? × ???? -?? ???? ] (a) About 1.2 (b) About 2.4 (c) About 3.6 (d) About 4.8 Ans: (b) ?? = constant., ?? = constant. So ?? = constant ? ?? ?? ?? ?? ?? ?? = ?? ???? ?? ???? ?? ???? ? ?? ?? ?? ?? ?? ?? 2 = ?? ???? ?? ???? ?? ???? 2 ? ?? ?? ?? ???? = v ?? ?? ?? ???? = v 1.0 × 10 -7 1.7 × 10 -8 = v 100 17 ˜ 2.4 Q9: Masses of three wires are in the ratio ?? : ?? : ?? and their lengths are in the ratio ?? : ?? : ?? . The ratio of their electrical resistance is (a) ?? : ?? : ?? (b) ?? : ?? : ?? (c) ?? : ???? : ?????? (d) ?????? : ???? : ?? Ans: (d) ?? = ?? ?? ?? = ?? ?? 2 ?? = ?? ?? 2 ?? ?? (? ?? = ?? ?? ) ?? 1 : ?? 2 : ?? 3 = ?? 1 2 ?? 1 : ?? 2 2 ?? 2 : ?? 3 2 ?? 3 = 25: 9 3 : 1 5 = 125: 15: 1 Q10: Two resistance ?? ?? and ?? ?? provides series to parallel equivalents as ?? ?? then the correct relationship is (a) ( ?? ?? ?? ?? ) ?? + ( ?? ?? ?? ?? ) ?? = ?? ?? (b) ( ?? ?? ?? ?? ) ?? /?? + ( ?? ?? ?? ?? ) ?? /?? = ?? ?? /?? (c) ( ?? ?? ?? ?? ) + ( ?? ?? ?? ?? ) = ?? (d) ( ?? ?? ?? ?? ) ?? /?? + ( ?? ?? ?? ?? ) ?? /?? = ?? ?? /?? Ans: (d) Series resistance ?? ?? = ?? 1 + ?? 2 and parallel resistance ?? ?? = ?? 1 ?? 2 ?? 1 +?? 2 ? ?? ?? ?? ?? = (?? 1 +?? 2 ) 2 ?? 1 ?? 2 = ?? ? ?? 1 + ?? 2 v?? 1 ?? 2 = v ?? ? v?? 1 2 v?? 1 ?? 2 + v?? 2 2 v?? 1 ?? 2 = v ?? ? v ?? 1 ?? 2 + v ?? 2 ?? 1 = v ?? Q11: Five resistances are combined according to the figure. The equivalent resistance between the point ?? and ?? will be (a) ?????? (b) ?????? (c) ?????? (d) ?????? Ans: (a) The equivalent circuit of above can be drawn as Which is a balanced wheatstone bridge. So current through ???? is zero. So 1 ?? = 1 20 + 1 20 = 1 10 ? ?? = 10O Q12: What will be the equivalent resistance of circuit shown in figure between points ?? and ?? [c (a) ?????? (b) ?????? (c) ?????? (d) ?????? Ans: (c) The equivalent circuit of above fig between ?? and ?? can be drawn as So ?? ???? = 10 + 10 + 10 = 30O Page 5 JEE Solved Examples on Current Electricity JEE Mains Q1: In the Bohr's model of hydrogen atom, the electrons moves around the nucleus in a circular orbit of a radius ?? × ???? -???? metre. It's time period is ?? . ?? × ???? -???? ?????? . The current associated is (a) Zero (b) ?? . ?? × ???? -???? ?? (c) ?? . ???? ?? (d) ?? . ???? × ???? -?? ?? Ans: (d) ?? = ?? ?? = 1.6×10 -19 1.5×10 -16 = 1.07 × 10 -3 A Q2: A copper wire of length ?? ?? and radius ?? ???? is joined in series with an iron wire of length ?? ?? and radius ?? ???? and a current is passed through the wire. The ratio of current densities in the copper and iron wire is (a) ???? : ?? (b) ?? : ?? (c) ?? : ?? (d) ?? : ?? Ans: (b) We know ?? = ?? ?? when ?? = constant ?? ? 1 ?? ? ?? ?? ?? ?? = ?? ?? ?? ?? = ( ?? ?? ?? ?? ) 2 = ( 3 1 ) 2 = 9 1 Q3: 8 In a wire of circular cross-section with radius ?? , free electrons travel with a drift velocity ?? , when a current ?? flows through the wire. What is the current in another wire of half the radius and of the some material when the drift velocity is ?? ?? (a) ?? ?? (b) ?? (c) ?? /?? (d) ?? /?? Ans: (c) ?? = ?????? ?? ?? = ?????? ?? 2 ?? and ?? 2 = ?????? ( ?? 2 ) 2 · 2?? = ?????? · 2 ?? 2 = ?? 2 Q4: Two wires ?? and ?? of the same material, having radii in the ratio ?? : ?? and carry currents in the ratio ?? : ?? . The ratio of drift speeds of electrons in ?? and ?? is (a) ???? : ?? (b) ?? : ???? (c) ?? : ?? (d) ?? : ?? Ans: (a) As ?? = ?????? ?? ?? ? ?? 1 ?? 2 = ?? 1 ?? 2 × ?? ?? 1 ?? ?? 2 = ?? 1 2 ?? 2 2 · ?? ?? 1 ?? ?? 2 ? ?? ?? 1 ?? ?? 2 = 16 1 Q5: Two wires of resistance ?? ?? and ?? ?? have temperature co-efficient of resistance ?? ?? and ?? ?? respectively. These are joined in series. The effective temperature co -efficient of resistance is (a) ?? ?? +?? ?? ?? (b) v ?? ?? ?? ?? (c) ?? ?? ?? ?? +?? ?? ?? ?? ?? ?? +?? ?? (d) v?? ?? ?? ?? ?? ?? ?? ?? v?? ?? ?? +?? ?? ?? Ans: (c) Suppose at ?? ° C resistances of the two wires becomes ?? 1?? and ?? 2?? respectively and equivalent resistance becomes ?? ?? . In series grouping ?? ?? = ?? 1?? + ?? 2?? , also ?? 1?? = ?? 1 (1 + ?? 1 ?? ) and ?? 2?? = ?? 2 (1 + ?? 2 ?? ) ?? ?? = ?? 1 (1 + ?? 1 ?? ) + ?? 2 (1 + ?? 2 ?? ) = (?? 1 + ?? 2 ) + (?? 1 ?? 1 + ?? 2 ?? 2 )?? = (?? 1 + ?? 2 )[1 + ?? 1 ?? 1 + ?? 2 ?? 2 ?? 1 + ?? 2 ?? ] . Hence effective temperature co -efficient is ?? 1 ?? 1 +?? 2 ?? 2 ?? 1 +?? 2 . Q6: A rod of certain metal is ?? ?? long and ?? . ?? ???? in diameter. It's resistance is ?? × ???? -?? ?? . A disc of the same metal is ?? ???? thick and ?? ???? in diameter, what is the resistance between it's circular faces. (a) ?? . ???? × ???? -?? ?? (b) ?? . ?? × ???? -?? ?? (c) ?? . ???? × ???? -?? ?? (d) ?? . ?? × ???? -?? ?? Ans: (b) By using ?? = ?? · ?? ?? ; ?? disc ?? rod = ?? disc ?? rod × ?? rod ?? disc ? ?? disc 3×10 -3 = 10 -3 1 × ?? (0.3×10 -2 ) 2 ?? (10 -2 ) 2 ? ?? disc = 2.7 × 10 -7 O. Q7: If a copper wire is stretched to make it ?? . ?? % longer, the percentage increase in resistance will be (a) 0.2 (b) 2 (c) 1 (d) 0.1 Ans: (a) In case of streching ?? ? ?? 2 So ??? ?? = 2 ??? ?? = 2 × 0.1 = 0.2 Q8: Equal potentials are applied on an iron and copper wire of same length. In order to have same current flow in the wire, the ratio ( ?? iron ?? copper ) of their radii must be [Given that specific resistance of iron = ?? . ?? × ???? -?? ???? and that of copper = ?? . ?? × ???? -?? ???? ] (a) About 1.2 (b) About 2.4 (c) About 3.6 (d) About 4.8 Ans: (b) ?? = constant., ?? = constant. So ?? = constant ? ?? ?? ?? ?? ?? ?? = ?? ???? ?? ???? ?? ???? ? ?? ?? ?? ?? ?? ?? 2 = ?? ???? ?? ???? ?? ???? 2 ? ?? ?? ?? ???? = v ?? ?? ?? ???? = v 1.0 × 10 -7 1.7 × 10 -8 = v 100 17 ˜ 2.4 Q9: Masses of three wires are in the ratio ?? : ?? : ?? and their lengths are in the ratio ?? : ?? : ?? . The ratio of their electrical resistance is (a) ?? : ?? : ?? (b) ?? : ?? : ?? (c) ?? : ???? : ?????? (d) ?????? : ???? : ?? Ans: (d) ?? = ?? ?? ?? = ?? ?? 2 ?? = ?? ?? 2 ?? ?? (? ?? = ?? ?? ) ?? 1 : ?? 2 : ?? 3 = ?? 1 2 ?? 1 : ?? 2 2 ?? 2 : ?? 3 2 ?? 3 = 25: 9 3 : 1 5 = 125: 15: 1 Q10: Two resistance ?? ?? and ?? ?? provides series to parallel equivalents as ?? ?? then the correct relationship is (a) ( ?? ?? ?? ?? ) ?? + ( ?? ?? ?? ?? ) ?? = ?? ?? (b) ( ?? ?? ?? ?? ) ?? /?? + ( ?? ?? ?? ?? ) ?? /?? = ?? ?? /?? (c) ( ?? ?? ?? ?? ) + ( ?? ?? ?? ?? ) = ?? (d) ( ?? ?? ?? ?? ) ?? /?? + ( ?? ?? ?? ?? ) ?? /?? = ?? ?? /?? Ans: (d) Series resistance ?? ?? = ?? 1 + ?? 2 and parallel resistance ?? ?? = ?? 1 ?? 2 ?? 1 +?? 2 ? ?? ?? ?? ?? = (?? 1 +?? 2 ) 2 ?? 1 ?? 2 = ?? ? ?? 1 + ?? 2 v?? 1 ?? 2 = v ?? ? v?? 1 2 v?? 1 ?? 2 + v?? 2 2 v?? 1 ?? 2 = v ?? ? v ?? 1 ?? 2 + v ?? 2 ?? 1 = v ?? Q11: Five resistances are combined according to the figure. The equivalent resistance between the point ?? and ?? will be (a) ?????? (b) ?????? (c) ?????? (d) ?????? Ans: (a) The equivalent circuit of above can be drawn as Which is a balanced wheatstone bridge. So current through ???? is zero. So 1 ?? = 1 20 + 1 20 = 1 10 ? ?? = 10O Q12: What will be the equivalent resistance of circuit shown in figure between points ?? and ?? [c (a) ?????? (b) ?????? (c) ?????? (d) ?????? Ans: (c) The equivalent circuit of above fig between ?? and ?? can be drawn as So ?? ???? = 10 + 10 + 10 = 30O Q13: Four resistances ?????? , ???? , ???? and ???? are connected so that they form the sides of a rectangle ???? , ???? , ???? and ???? respectively. Another resistance of ?????? is connected across the diagonal ???? . The equivalent resistance between ?? &?? is (a) ???? (b) ???? (c) ???? (d) ?????? Ans: (b) Q14: In the combination of resistances shown in the figure the potential difference between ?? and ?? is zero, when unknown resistance (?? ) is (a) ???? (b) ???? (c) ???? (d) The emf of the cell is required Ans: (b) The potential difference across ?? , ?? will be zero, when the circuit will act as a balanced wheatstone bridge and ?? ?? = ?? ?? ? 12+4 ?? = 1+3 1/2 ? ?? = 2ORead More
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Solved Example: Current Electricity JEE Questions
The "Solved Example: Current Electricity JEE Questions" guide is a valuable resource for all aspiring students preparing for the
JEE exam. It focuses on providing a wide range of practice questions to help students gauge
their understanding of the exam topics. These questions cover the entire syllabus, ensuring comprehensive preparation.
The guide includes previous years' question papers for students to familiarize themselves with the exam's format and difficulty level.
Additionally, it offers subject-specific question banks, allowing students to focus on weak areas and improve their performance.
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The content of Solved Example: Current Electricity is prepared as per the latest JEE syllabus.
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