Question
A student demonstrates electromagnetic induction.
(a) Describe how to demonstrate electromagnetic induction using a magnet, a coil of wire and a sensitive ammeter. You may include a diagram.
(b) State two factors that affect the size of an induced electromotive force (e.m.f.)
1.
2.
Answer/Explanation
Answer:
(a) coil of wire connected in series with (sensitive) ammeter
magnet moves relative to coil
meter indicates/measures (induced) current
(b) Any two from:
speed of movement owtte
strength of magnet
number of coils/turns per metre
Question
A charger for a cellphone (mobile phone) is marked:
input: a.c. 240 V, 50 Hz, 80 mA.
output: d.c. 5.3 V, 500 mA.
(a) State
(i) the component in the charger that converts a.c. to d.c.,
(ii) the quantity that has the value 50 Hz.
(b) Calculate
(i) the output power of the charger,
output power =
(ii) the energy transferred in the output circuit when the cellphone is charged for 1.5 hours.
energy =
(c) In the following list, underline the quantity that is stored in the battery of the cellphone.
voltage current power energy
Answer/Explanation
Answer:
(a) (i) rectifier/ diode
(ii) frequency (of A.C. supply)
(b) (i) (P =) IV OR 0.5 × 5.3 OR 500 × 5.3
2.6W OR 2600mW
(ii) (E =) Pt OR IVt OR 2.65 × 1.5 × 3600 OR 0.5 × 5.3 × 1.5 × 3600
14000J
(c) energy only underlined
Question
(a) A student changes the current in a filament lamp. She measures the current and the potential difference (p.d.) across the lamp.
Fig. 11.1 is an incomplete circuit diagram.
(i) On Fig. 11.1, complete the unfinished circuit symbols.
(ii) One pair of readings for the lamp is shown in the table.
p.d./ V | current /A |
6.0 | 1.2 |
Calculate the resistance of the filament in the lamp for these readings.
resistance of filament = ……………………………………………………..Ω
(iii) After many hours of use, the filament wire in a lamp becomes thinner.
State the effect, if any, on the resistance of the lamp.
(b) (i) Complete the circuit in Fig. 11.2 to show a battery connected to three lamps arranged in parallel.
(ii) Describe two advantages of connecting these lamps in parallel with the battery.
Answer/Explanation
Answer:
(a) (i) ammeter correct symbol in series with lamp
voltmeter correct symbol in parallel with lamp
lamp correct symbol
(ii) R = V/ I in any form
6 ÷ 1.2
5(Ω)
(iii) (resistance) increases
(b) (i) 3 lamp symbols drawn
(lamps connected) in parallel with battery
(ii) any two from:
• lamps all have 6V or full voltage (across them)
• if one (lamp) breaks, others continue to operate/ little/ no effect on others
• lamps can be switched on and off independently