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## 章节主题：

Electrical current
Potential difference
Resistance and resistivity
Electromotive force

## 学习目标：

(a) Show an understanding that electric current is the rate of flow of charge.

(b) Derive and use the equation I = nAvq for a current-carrying conductor, where n is the number density of charge carriers and v is the drift velocity.

(c) Recall and solve problems using the equation Q = It

(d) Recall and solve problems using the equation V = W/Q

(e) Recall and solve problems using the equations P = VI, P = I²R and P = V²/R.

(f) Define the resistance of a circuit component as the ratio of the potential difference across the component to the current passing through it and solve problems using the equation V = IR.

(g) Sketch and explain the I–V characteristics of various electrical components such as an ohmic resistor, a semiconductor diode, a filament lamp and a negative temperature coefficient (NTC) thermistor.

(h) Sketch the resistance-temperature characteristic of an NTC thermistor.

(i) Recall and solve problems using the equation R =ρl/A.

(j) Distinguish between electromotive force (e.m.f.) and potential difference (p.d.) using energy considerations.

(k) Show an understanding of the effects of the internal resistance of a source of e.m.f. on the terminal potential difference and output power.

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