2.Electricity

Question 1

U16PH5 Explain why the 6.0µF capacitor stores the same amount of energy as one of the 1.5µF capacitors. [2]

Answer 1

Question 2

U10PH5 Explain briefly whether or not the time the capacitor takes to lose half its energy is longer or shorter than to lose half its charge.

Answer 2

Question 3

A09PH1 (ii) State the sign of the charge acquired by the duster. Explain your reasoning. [2]

Answer 3

Electrons transferred from [polythene] rod to [metal cap] [or equiv] [Not just −ve charge]

+ve (1) because electrons [accept: negative charges] transferred from duster to rod (1).

Question 4

V = E – Ir (a) Explain carefully, in terms of energy, the meanings of V, E and Ir. [4]

Answer 4

‘per unit charge’ [or ‘per coulomb’] used correctly at least once. (1)

V = energy delivered [per unit charge] to [external] circuit (1)

E = energy supplied [per unit charge] from chemical energy of cell (1)

Ir = energy wasted / lost / dissipated [per coulomb] in the internal resistance (1)

Question 5

(a) What is a superconductor? [1]

Answer 5

A material with zero/negligible resistance

Question 6

(c) Conducting electrons in a superconductor do not cause a heating effect. Explain why conducting electrons do produce a heating effect in wires at room temperature. [2]

Answer 6

Collisions between free/delocalised/flowing/conducting electrons and ions/atoms in lattice/atoms/particles (1)

increase vibrations of ions /atoms / particles or electrons transfer KE to ions (1)

Question 7

(ii) why the terminal pd drops when the battery supplies a current. [1]

Answer 7

Energy lost in the resistance of cell