1. A single wire carries the same current through a wide section (A=18×10⁻⁶ m²) and a narrow section (A=2×10⁻⁶ m²). Find the ratio v_d(narrow)/v_d(wide).
- 18
- 9
- 1/9
- 4.5
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Electric Current, Drift Velocity and Ohm's Law · Class XII / Second PUC
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Mode: BalancedQuestions: 18Difficulty: MixedCheck code: 179417190
2. A copper wire (n=8.5×10²⁸ per m³) has cross-sectional area 1×10⁻⁶ m² and carries a current of 3.4 A. Find the drift velocity, then find the time taken for an electron to drift 1 m along the wire (assume the drift velocity stays constant). Use e=1.6×10⁻¹⁹ C.
- v_d=2.5×10⁻⁴ m/s; time≈4000 s (≈66.7 min)
- v_d=2.5×10⁻⁴ m/s; time≈400 s
- v_d=4×10³ m/s; time≈2.5×10⁻⁴ s
- v_d=2.5×10⁻⁴ m/s; time≈40000 s
3. A resistor's resistance is found to increase noticeably as more current is passed through it, due to self-heating. Strictly speaking, over this range of increasing current, is the resistor's V-I behavior perfectly ohmic?
- Yes, as long as V and I are both positive
- Cannot be determined without knowing the exact resistance values
- No — R must stay constant for the behavior to be strictly ohmic, and here it's changing due to heating
- Yes, since V=IR can still be computed at each point
4. A charge of 104 C flows through a wire in 8 seconds. Find the current.
- 13 A
- 0.077 A
- 832 A
- 96 A
5. A wire has n=1×10²⁸ per m³, A=4×10⁻⁶ m², carrying a current of 3.2 A. Find the drift velocity. Use e=1.6×10⁻¹⁹ C.
- 5×10⁻⁵ m/s
- 5×10⁻⁴ m/s
- 1×10⁻⁴ m/s
- 2.5×10⁻⁴ m/s
6. A conductor draws 3 A at 33 V, and 7 A at 77 V. Verify Ohm's Law and find R.
- Ohmic, R=11 Ω
- Non-ohmic
- Ohmic, R=7 Ω
- Ohmic, R=22 Ω
7. A current of 4 A flows in one direction for 90 s, then reverses direction and flows at 3 A for the next 60 s. Taking the original direction as positive, find the NET charge transferred.
- −180 C
- 180 C
- 540 C
- 360 C
8. A component's resistance R(T) increases with temperature: at 20°C, R=8 Ω; at 70°C, R=13 Ω. If it carries exactly 2 A at 70°C, find the voltage across it at that temperature, and state whether the device behaves as strictly ohmic across this temperature range.
- 13 V; not ohmic
- 26 V; not strictly ohmic across this temperature range, since R itself changes
- 16 V; ohmic across the range
- 26 V; ohmic across the range, since V=IR was still used correctly
9. A current of 5 A flows through a wire for 2 minutes, then increases to 8 A for the next 3 minutes. Find the total charge that has flowed.
- 600 C
- 1040 C
- 2040 C
- 1440 C
10. A wire carries a current that grows linearly with time: I(t)=2t (in amperes, t in seconds), starting from t=0. Find the total charge that flows between t=0 and t=5 s.
- 50 C
- 5 C
- 25 C
- 10 C
11. A wire narrows uniformly from area A₁=12×10⁻⁶ m² to area A₂=3×10⁻⁶ m² over its length, carrying a steady current of 6 A throughout. Find the current density J₂ at the narrow end, and the ratio J₂/J₁.
- J₂=2×10⁶ A/m², ratio J₂/J₁=4
- J₂=5×10⁵ A/m², ratio=1
- J₂=2×10⁶ A/m², ratio=0.25
- J₂=8×10⁶ A/m², ratio=16
12. Inside a battery's external circuit, electrons flow from the negative terminal, through the wire, to the positive terminal. In which direction is conventional current considered to flow through this EXTERNAL circuit?
- From the negative terminal to the positive terminal, matching electron flow
- There is no conventional current in this case
- Conventional current only exists inside the battery
- From the positive terminal, through the wire, to the negative terminal
13. A conductor's resistance is measured to be 6 Ω. As current is increased from 2 A to 10 A, the voltage across it is measured at several points, and the V-I graph turns out to be a PERFECT straight line through the origin throughout this entire range. What can be concluded?
- R must be changing even though the graph looks straight
- More data is needed regardless of the straight-line result
- The conductor IS ohmic across this entire current range, with R=6 Ω throughout
- The conductor cannot be ohmic since current varies so much
14. A wire of cross-sectional area 4×10⁻⁶ m² carries a current of 20 A. Find the current density.
- 1×10⁷ A/m²
- 5×10⁵ A/m²
- 5×10⁶ A/m²
- 2.5×10⁶ A/m²
15. Two wires, X and Y, made of the same metal (same n) carry the same current, but wire X has twice the cross-sectional area of wire Y. Compare their drift velocities.
- Drift velocity in X is half that in Y
- Drift velocity in X is double that in Y
- They are equal
- Cannot be determined without more information
16. How many electrons flow past a cross-section per second in a wire carrying exactly 3.2 A? Use e=1.6×10⁻¹⁹ C.
- 6.25×10¹⁸ electrons/s
- 3.2×10⁻¹⁹ electrons/s
- 2×10¹⁸ electrons/s
- 2×10¹⁹ electrons/s
17. A wire tapers uniformly so that its cross-sectional area varies with position x as A(x)=A₀(1+x) (x in metres, A₀=2×10⁻⁶ m²), carrying a steady current of 8 A. Find the current density at x=0 and at x=3 m.
- J(0)=1×10⁶ A/m², J(3)=4×10⁶ A/m²
- J(0)=4×10⁶ A/m², J(3)=4×10⁶ A/m² (unchanged)
- J(0)=8×10⁶ A/m², J(3)=2×10⁶ A/m²
- J(0)=4×10⁶ A/m², J(3)=1×10⁶ A/m²
18. A wire's free electron density is 5×10²⁸ per m³ and its cross-sectional area is 2.5×10⁻⁶ m². If the drift velocity is measured to be 4×10⁻⁴ m/s, find the current flowing, then find how many electrons pass a given cross-section every second. Use e=1.6×10⁻¹⁹ C.
- I=8 A, 1.25×10¹⁹ electrons/s
- I=1.25×10²³ A, 5×10¹⁹ electrons/s
- I=8 A, 8×10¹⁹ electrons/s
- I=8 A, 5×10¹⁹ electrons/s