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Knox Academy Higher Physics

AC and Capacitance Homework 1

Answer all questions.

1. The output from a signal generator is

connected to the input terminals of an

oscilloscope. The trace observed on the

oscilloscope screen, the Y-gain setting and

the time base setting are shown in the

diagram.

The frequency of the signal shown is

calculated using the

A Y-gain setting and the vertical height

of the trace.

B Y-gain setting and the horizontal

distance between the peaks of thetrace.

C Y-gain setting and the time base

setting.

D Time base setting and the vertical

height of the trace.

E Time base setting and the horizontal

distance between the peaks of the

trace.

2. An a.c. signal is displayed on an oscilloscope

screen. The Y-gain and time base controls

are set as shown.

The frequency of the signal is

A 0.5Hz

B 1.25Hz

C 2.00Hz

D 200Hz

E 500Hz

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3. A trace of an electrical signal on the screen

of an oscilloscope is shown below.

The time base is set at 50mscm-1.

If the time base setting is doubled, the

number of waves on the screen is:

A 1

B 2

C 2.5

D 5

E 10

5. An alternating voltage signal is displayed

on an oscilloscope, with the settings

shown.

Which row in the following table gives the

correct values for the peak voltage and

frequency of the signal?

Peak voltage

(V)

Frequency

(Hz)

A 10 100

B 10 250

C 20 250

D 10 500

E 20 1000

4. An immersion heater can be operated either

from an a.c. supply or a d.c. supply. The

graph below represents the a.c. supply

voltage.

What d.c. supply voltage would produce the

same rate of heating from this heater?

6. The heating element in a boiler operates at

2400W from a 120V r.m.s. power supply.

What is the r.m.s. current, in amperes, in thiselement?

7. The step up transformer shown below is

used to light a mains lamp at its correct

rating. The input voltage to the primary is

6V r.m.s. and the voltage across the lamp is

240V r.m.s.

The a.c. ammeters A1 and A2 have

negligible resistance.

The reading on A1 is 5.0A r.m.s. and the

reading on A2 is 0.1A r.m.s.

The efficiency of the transformer is

A 2.5%

B 40%

C 50%

D 80%

E 100%

9. The output from an electrical device produces

the following trace on an oscilloscope.

The time base setting of the oscilloscope is

2ms per division and the voltage gain setting

is 5mV per division.

What is the frequency and maximum voltage

of the output from this device?

Frequency of the

device

(Hz)

Maximum voltage

output from the

device

(mV)

A 33 15

B 83 15

C 83 30

D 166 30

E 166 15

8. What is the relationship between the r.m.s.

and peak values for an alternating current?

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10. An oscilloscope trace of a 230V, 125Hz a.c. power supply is shown below.

(a) (i) Calculate the peak voltage of the supply. 2

(ii) Calculate the time base setting on the oscilloscope. 3

(b) A joiner uses the supply voltage to operate a lathe with a resistance of 800.

(i) Calculate the r.m.s. operating current of the lathe. 2

(ii) Calculate the power rating of the lathe. 2

(9)

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