WAEC Past Questions and Answers - Page 4189

20,941.

Evaluate \(\log_{10} 25 + \log_{10} 32 - \log_{10} 8\)

A.

0.2

B.

2

C.

100

D.

409

E.

490

Correct answer is B

\(\log_{10} 25 + \log_{10} 32 - \log_{10} 8\)

= \(\log_{10} (\frac{25 \times 32}{8})\)

= \(\log_{10} 100 \)

= 2

20,942.

Calculate the resistance of the filament of a lamp rates 240 V, 40 W

A.

240Ω

B.

360Ω

C.

720Ω

D.

1440Ω

E.

2880Ω

Correct answer is D

R = V2/P = 2402/40 = 1440Ω

20,943.

If the frequency of the ac. circuit illustrated above is 500/π Hz what would be the reactance in the circuit? 

(Inductance (L) = 0.9H, Capacitance (C) = \(2 \times 10^{-6}\)

A.

0.0009Ω/π

B.

100Ω

C.

1030Ω

D.

400Ω

E.

2500Ω

Correct answer is D

Given Data: Frequency (F) = \(\frac{500}{π}\) , Inductance (L) = 0.9H, Capacitance (C) = \(2 \times 10^{-6}\)

Total circuit reactance = Inductive reactance ( X\(_L\) ) - Capacitive reactance ( X\(_C\) )

when  ( X\(_L\) ) >  ( X\(_C\) )

Inductive reactance ( X\(_L\) ) = 2πFL = 2 \(\times\) π \(\times\) \(\frac{500}{π}\) \(\times\) 0.9 = 900Ω

Capacitive reactance ( X\(_C\) ) = \(\frac{1}{2πFC}\) = \(\frac{1}{2 \times π \times 500/π \times 2 \times 10^{-6}}\)

= \(\frac{1}{2 \times 10^{-3}}\) = \(\frac{1}{0.002}\)  

= 500Ω

 

Total circuit reactance =  ( X\(_L\) ) -  ( X\(_C\) ) = (900 - 500)Ω

=400Ω

20,944.

Simplify: \((\frac{16}{81})^{\frac{1}{4}}\)

A.

8/27

B.

1/3

C.

4/9

D.

2/3

E.

-4/3

Correct answer is D

\((\frac{16}{81})^{\frac{1}{4}}\)

= \(((\frac{2}{3})^{4})^{\frac{1}{4}}\)

= \(\frac{2}{3}\)

20,945.

The nth term of a sequence is given by 3.2\(^{n-2}\). Write down the first three terms of the sequence.

A.

2/3, 0, 6

B.

3/2, 3, 6,

C.

2/3, 3, 8/3

D.

2/3, 3/4, 6

E.

2/3, 3, 1/3

Correct answer is B

\(T_n = 3. 2^{n - 2} \)

\(T_{1} = 3. 2^{1 - 2} = 3. 2^{-1} \)

\(T_1 = \frac{3}{2} \)

\(T_2 = 3. 2^{2 - 2} \)

\(T_2 = 3. 2^0  = 3\)

\(T_3 = 3. 2^{3 - 2} = 3. 2^1 \)

\(T_3 = 6\)

The first 3 terms of the sequence are \(\frac{3}{2}\), 3 and 6.